POLYMERIZING ENZYMES FOR SEQUENCING REACTIONS

RELATED APPLICATIONS

This application claims priority under 35 U.S.S. § 119(e) to U.S. provisional patent application no. 62/868,806, filed June 28, 2019, and to U.S. provisional patent application no. 62/993,597, filed March 23, 2020, each of which is hereby incorporated by reference in its entirety.

BACKGROUND

DNA polymerases are nucleotide polymerizing enzymes that are essential for the replication of the genomes of all living organisms. In addition to their role in maintaining genome integrity during replication and repair, DNA polymerases are widely used for DNA manipulation in vitro , including DNA cloning, mutagenesis, and sequencing. The fundamental ability of DNA polymerases to synthesize a complementary strand according to a template DNA is conserved, although specific properties, including processivity, fidelity, and substrate nucleotide selectivity, differ among the enzymes.

SUMMARY

Aspects of the technology disclosed herein relate to modified polymerizing enzymes (e.g., polymerases) that may be used to conduct in vitro polymerization reactions. In some aspects, polymerases described herein are suitable for use in sequencing reactions (e.g., nucleic acid sequencing). In some aspects, the disclosure provides recombinant polymerases having one or more modifications. In some embodiments, recombinant polymerases of the disclosure comprise at least one of an amino acid mutation or a domain substitution.

In some aspects, the disclosure provides a modified polymerizing enzyme (e.g., a nucleic acid polymerizing enzyme, or a nucleic acid polymerase) having an amino acid sequence that is based on a naturally occurring polymerase (e.g., selected from TABLE 1) and that includes one or more amino acid mutations and/or segment substitutions. In some embodiments, a modified polymerizing enzyme has an amino acid sequence that is based on E. faecium polymerase (SEQ ID Nos: 2-5). In some embodiments, a modified polymerizing enzyme has an amino acid sequence that is based on SEQ ID Nos: 23-33. In some embodiments, a modified polymerizing enzyme comprises one or more segment substitutions (e.g., wherein one or more segments of a polymerase are replaced with one or more corresponding segments from a different polymerase), one or more amino acid additions, deletions, and/or substitutions, or a combination thereof. In some embodiments, a segment comprises a defined region of a polymerase (e.g., a structural or functional domain or subdomain), or a portion thereof, and optionally including one or more flanking amino acids (e.g., 1-50, 1-40, 1-30, 1-20, 1-10, 1-5, 5-10, 5-25, or any integral number within these ranges of amino acids on either side of a region or portion thereof, for example in a naturally-occurring polymerase of TABLE 1, e.g., SEQ ID Nos: 2-5 or SEQ ID Nos: 23-33). In some embodiments, one or more amino acid insertions, deletions, or substitutions correspond to naturally occurring differences between two naturally-occurring polymerases at one or more positions. In some embodiments, one or more amino acid insertions, deletions, or substitutions are new non-naturally occurring changes. In some embodiments, an amino acid substitution is a conservative amino acid substitution (e.g., replacing one amino acid with another amino acid having similar properties, for example having similar charged, polar, hydrophobic, hydrophilic, and/or other similar properties such as similar size). In some embodiments, an amino acid substitution is a non-conservative amino acid substitution. In some embodiments, one or more amino acid insertions, deletions, or substitutions can be at any position(s) in a modified polymerase, including in one or more swapped segments from different polymerases and/or in segments of the original polymerase.

Accordingly, in some embodiments the disclosure provides a recombinant polymerizing enzyme having an amino acid sequence selected from TABLE 1, e.g., SEQ ID Nos: 2-5 or SEQ ID Nos: 23-33 (or having an amino acid sequence that has at least 50%, at least 60%, at least 70%, at least 80%, 80-90%, 90-95%, 95-99%, or higher amino acid sequence identity to an amino acid sequence selected from TABLE 1, e.g., SEQ ID Nos: 2-5 or SEQ ID Nos: 23-33) and comprising one or more amino acid modifications from TABLE 2, TABLE 3, TABLE 4,

TABLE 5, TABLE 6, or TABLE 7. In some embodiments, the one or more amino acid modifications include at least one amino acid mutation (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20,

25, or more amino acid mutations). In some embodiments, the one or more amino acid modifications include at least 1 and up to 5 amino acid mutations, at least 1 and up to 10 amino acid mutations, at least 1 and up to 15 amino acid mutations, at least 1 and up to 25 amino acid mutations, at least 1 and up to 50 amino acid mutations, or at least 1 and up to 100 amino acid mutations. In some embodiments, the one or more amino acid modifications include at least one domain substitution (e.g., a substitution of an entire domain or a substitution of a segment that encompasses a domain or a portion of a domain). In some embodiments, the at least one domain substitution comprises at least one of an exonuclease domain substitution and a polymerase domain substitution. In some embodiments, an exonuclease domain substitution comprises an exonuclease loop substitution. In some embodiments, a polymerase domain substitution comprises any one of a palm subdomain substitution, a TPR1 subdomain substitution, a fingers subdomain substitution, a TPR2 subdomain substitution, or a thumb subdomain substitution (e.g., a substitution of an entire polymerase, palm, TPR1, fingers, TPR2, or thumb domain or subdomain, or a portion of any one thereof, optionally including one or more flanking amino acids). In some embodiments, the one or more amino acid modifications include at least one domain substitution and at least one amino acid mutation. In some embodiments, an amino acid mutation can be an amino acid insertion, deletion, or substitution.

In some embodiments, a recombinant polymerizing enzyme of the disclosure has a sequence selected from TABLE 2. In some embodiments, the disclosure provides a recombinant polymerizing enzyme having a sequence selected from TABLE 3. In some embodiments, the disclosure provides a recombinant polymerizing enzyme having a sequence selected from

TABLE 4. In some embodiments, the disclosure provides a recombinant polymerizing enzyme having a combination of modification listed in TABLE 7.

In some aspects, the disclosure provides a recombinant polymerizing enzyme comprising a segment that includes an exonuclease region or a portion thereof (and optionally flanking amino acids on one or both sides) of any one of recombinant polymerizing enzymes in TABLE 1 (e.g., SEQ ID Nos: 2-5 or SEQ ID Nos: 23-33). In some aspects, the disclosure provides a recombinant polymerizing enzyme comprising a segment that includes a palm region or a portion thereof (and optionally flanking amino acids on one or both sides) of any one of recombinant polymerizing enzymes in TABLE 1 (e.g., SEQ ID Nos: 2-5 or SEQ ID Nos: 23-33). In some aspects, the disclosure provides a recombinant polymerizing enzyme comprising a segment that includes a TPR1 region or a portion thereof (and optionally flanking amino acids on one or both sides) of any one of recombinant polymerizing enzymes in TABLE 1 (e.g., SEQ ID Nos: 2-5 or SEQ ID Nos: 23-33). In some aspects, the disclosure provides a recombinant polymerizing enzyme comprising a segment that includes a fingers region or a portion thereof (and optionally flanking amino acids on one or both sides) of any one of recombinant polymerizing enzymes in TABLE 1 (e.g., SEQ ID Nos: 2-5 or SEQ ID Nos: 23-33). In some aspects, the disclosure provides a recombinant polymerizing enzyme comprising a segment that includes a TPR2 region or a portion thereof (and optionally flanking amino acids on one or both sides) of any one of recombinant polymerizing enzymes in TABLE 1 (e.g., SEQ ID Nos: 2-5 or SEQ ID Nos: 23-33). In some aspects, the disclosure provides a recombinant polymerizing enzyme comprising a segment that includes a thumb region or a portion thereof (and optionally flanking amino acids on one or both sides) of any one of recombinant polymerizing enzymes in TABLE 1 (e.g., SEQ ID Nos: 2-5 or SEQ ID Nos: 23-33). In some aspects, the disclosure provides a recombinant polymerizing enzyme comprising two or more segments as described herein.

Accordingly, in some embodiments, a recombinant polymerizing enzyme is a chimeric enzyme that comprises one or more amino acid segments from different polymerizing enzymes (e.g., from a different species). In some embodiments, a chimeric polymerase comprises an amino acid sequence from a first polymerizing enzyme in which one or more segments have been replaced with segment(s) from different polymerizing enzymes. In some embodiments, the one or more segments from different polymerizing enzymes can be a segment comprising amino acids 1-51 from the M2Y polymerase, a segment comprising amino acids 271-375 from the E. faecium polymerase, a segment comprising amino acids 72-89 from the E. faecium polymerase, and/or a segment comprising amino acids 445-449 from the E. faecium polymerase. In some embodiments, the 1-51 segment from M2Y polymerase replaces a corresponding naturally occurring polymerase segment (e.g., amino acids 1-54 of F29 polymerase). In some

embodiments, the 271-375 segment from E. faecium polymerase replaces a corresponding naturally occurring polymerase segment (e.g., amino acids 260-359 of F29 polymerase). In some embodiments, the 72-89 segment from E. faecium polymerase replaces a corresponding naturally occurring polymerase segment (e.g., amino acids 75-91 of F29 polymerase). In some embodiments, the 445-449 segment from E. faecium polymerase replaces a corresponding naturally occurring polymerase segment (e.g., amino acids 429-433 of F29 polymerase).

In some embodiments, a recombinant polymerizing enzyme comprises one or more substitutions corresponding to the following substitutions in F29: M8R, V51A, N62D, 17 IV,

LI 071, K131E, K135Q, L142K, G197D, Y224K, E239G, V250A/I, L253A/H, Y281H, I288L, T301C, R306Q, R308L, D325E, D341E, K354R, T368F, E375Y, A437G, A444T, E466K, D476H, A484E, E508R, D510K/R, K512Y, E515Q, K539E, D570S, and T571V.

In some embodiments, a recombinant polymerizing enzyme comprises one or more substitutions corresponding to the following substitutions in E. faecium: K4R, S22A, N59D, E60L, E85P, N106G, Q122V, P136T, E139K/Q, E142K/Q, I148K, D167P, D171K, D189K, T211A, D232K, V261A/I, L264A/H/M, T479V, E482K, D492H, S493P, K500E, Q513D, E519R, D521K/R, E523K/Y, R308G, S319L, L320M, E323V, D337G, E338K, D341T, I384F/S, E391Y/W/F/H/M/K/R, L437Y, E537K, T568S, and M569V.

In some embodiments, a modified polymerase comprises one or more of the segment substitutions and/or amino acid insertions, deletions, and/or substitutions described herein, and also comprises one or more (e.g., 1-5, 5-10, 10-25, 25-50, 50-75, 75-100, 100-125, 125-150) additional amino acid insertions, deletions, and/or substitutions (e.g., conservative or non- conservative amino acid substitutions). Accordingly, in some embodiments, a modified polymerase of TABLE 2, TABLE 3, or TABLE 4 can include one or more additional (e.g., 1-5, 5-10, 10-25, 25-50, 50-75, 75-100, 100-125, 125-150) additional amino acid insertions, deletions, and/or substitutions (e.g., conservative or non-conservative amino acid substitutions).

In some aspects, the disclosure relates to modified recombinant enzymes comprising a first segment and a second segment, wherein: the first segment comprises an amino acid sequence corresponding to a first reference segment, said first reference segment containing amino acids 197-271 of SEQ ID NO: 2, wherein the amino acid sequence of the first segment is at least 80%, 80-90%, 90-95%, or at least 95% identical to the amino acid sequence of the first reference segment, and wherein the first segment has a higher isoelectric point than the first reference segment; and the second segment comprises an amino acid sequence corresponding to a second reference segment, said second reference segment containing amino acids 443-528 of SEQ ID NO: 2, wherein the amino acid sequence of the second segment is at least 80%, 80-90%, 90-95%, or at least 95% identical to the amino acid sequence of the second reference segment, and wherein the second segment has a higher isoelectric point than the second reference segment. In particular embodiments, the first segment comprises an amino acid sequence that is at least 80%, 80-90%, 90-95%, or at least 95% identical to 197-271 of SEQ ID NO: 2 and the second segment comprises an amino acid sequence that is at least 80%, 80-90%, 90-95%, or at least 95% identical to amino acids 443-528 of SEQ ID NO: 2.

In some aspects, the disclosure relates to modified recombinant enzymes comprising a first segment comprising an amino acid sequence corresponding to a reference segment, said reference segment containing amino acids 1-196 of SEQ ID NO: 2, wherein the amino acid sequence of the first segment is at least 80%, 80-90%, 90-95%, or at least 95% identical to the amino acid sequence of the reference segment; and wherein the first segment has a higher isoelectric point than the reference segment. In particular embodiments, the first segment comprises an amino acid sequence that is at least 80%, 80-90%, 90-95%, or at least 95% identical to 1-196 of SEQ ID NO: 2.

In some aspects, the disclosure relates to modified recombinant enzymes comprising a first segment and a second segment, wherein: the first segment comprises an amino acid sequence corresponding to a first reference segment, said first reference segment containing amino acids 1-271 of SEQ ID NO: 2, wherein the amino acid sequence of the first segment is at least 80%, 80-90%, 90-95%, or at least 95% identical to the amino acid sequence of the first reference segment, and wherein the first segment has a higher isoelectric point than the first reference segment; and the second segment comprises an amino acid sequence corresponding to a second reference segment, said second reference segment containing amino acids 443-528 of SEQ ID NO: 2, wherein the amino acid sequence of the second segment is at least 80%, 80-90%, 90-95%, or at least 95% identical to the amino acid sequence of the second reference segment, and wherein the second segment has a higher isoelectric point than the second reference segment. In particular embodiments, the first segment comprises an amino acid sequence that is at least 80%, 80-90%, 90-95%, or at least 95% identical to 1-271 of SEQ ID NO: 2 and the second segment comprises an amino acid sequence that is at least 80%, 80-90%, 90-95%, or at least 95% identical to amino acids 443-528 of SEQ ID NO: 2.

In some embodiments, the amino acid sequence of the modified recombinant enzyme comprises a modification at one or more positions corresponding to K4, T13, S22, V25, C26, D27, N33, 134, F36, S42, D54, N59, E60, E65, E85, M95, N106, T110, T114, K119, Q122, Y133, P136, E139, E142, N145, P147, 1148, E152, 1153, P160, D167, D171, N175, F188, D189, Q206, T211, S216, R217, D232, A236, V247, 1253, V261, L264, S267, V443, L445, A446,

S447, V449, T450, W452, G453, Y455, F465, N467, T479, E482, A484, E485, A486, L490, D492, S493, K495, K500, S503, Q506, Q513, E519, D521, E523, and V526 of SEQ ID NO: 2.

In some embodiments, a modification is an amino acid substitution selected from the group consisting of K4R, T13N, S22A, V25L, C26W, D27E, N33T, I34V, F36V, S42T, D54Y, N59D, E60L, E60V, E65S, E85P, M95T, M95K, N106G, T110I, T114S, K119Q, Q122V, Y133L, P136T, E139K, E139Q, E139R, E139H, E142K, E142Q, E142R, E142H, N145K, N145H, N145R, P147Q, P147T, I148K, I148H, I148R, E152D, I153V, P160A, D167P, D167K, D167H, D167R, D171K, D171H, D171R, N175T, N175Y, F188C, D189K, D189H, D189R, Q206R, Q206K, Q206H, T211A, S216G, S216R, R217G, D232K, A236G, V247D, I253H, I253A, V261A, V261I, V261L, L264H, L264A, L264M, S267A, V443T, L445M, A446G, S447V, V449I, T450A, W452Y, G453A, Y455W, F465Y, N467R, N467K, N467H, N467S, N467T, T479V, E482K, E482H, E482R, A484E, E485D, A486E, L490M, D492H, D492K, D492R, D492A, H492S, S493P, K495R, K500E, S503A, S503T, Q506K, Q513D, D521K, D521R, D521H, E523R, E523V, E523Y, E523F, E523H, E523W, and V526L.

In some embodiments, the amino acid sequence of the modified recombinant enzyme comprises a modification at one or more positions corresponding to E139, E142, N145, 1148, D167, D171, D189, N467, E482, D492, K495, D521, and E523. In some embodiments, a modification is an amino acid substitution selected from the group consisting of E139K, E139Q, E139R, E139H, E142K, E142H, E142R, E142Q, N145K, N145H, N145R, I148K, I148H, I148R, D167P, D167K, D167H, D167R, D171K, D171H, D171R, D189K, D189H, D189R, N467R, N467K, N467H, N467S, N467T, E482K, E482H, E482R, D492H, D492K, D492R, K495R, D521K, D521H, D521R, E523K, E523Y, E523H, E523R, E523F, and E523W.

In some embodiments, the amino acid sequence of the modified recombinant enzyme comprises a modification at one or more positions corresponding to P273, P275, R308, V315, Q317, S319, L320, 1322, Q323, D337, E338, D341, T345, F352, F353, T364, D374, 1384, E385, N388, E391, A396, N397, G400, D414, D425, R429, E436, L437, D533, R534, E537, G547, E545, L555, P556, R558, T559, V564, T568, M569, and T571 of SEQ ID NO: 2. In some embodiments, a modification is an amino acid substitution selected from the group consisting of P273S, P273R, P275S, E283K, V315L, S319R, R308G, G308R, Q317R, S319R, L320M, L320T, I322K, Q323G, Q323V, Q323R, D337G, E338K, D341T, T345I, F352I, F353C, T364I, D374G, D374Q, D374H, I384T, I384F, I384S, E385Y, E385K, E385R, E385N, E385Q, E385L, E385A, N388T, E391Y, E391W, E391F, E391H, E391M, E391K, E391R, A396Q, N397L, G400L, D414V, D425N, R429G, E436R, E436G, L437Y, L437E, D533A, D533Q, D533T, D533R, D533S, R534K, E537K, E537H, E537R, E545K, E545H, E545R, G547S, L555K, L555R, P556A, R558H, T559V, V564L, T568D, T568S, M569K, M569T, M569V, and T571S. In some embodiments, a modification is an amino acid substitution selected from the group consisting of D374G, D374Q, D374H, E385Y, E385K, E385R, E385N, E385Q, E385L, E385A, E391Y, E391W, E391K, E391F, D533A, D533Q, D533T, D533R, D533S, E537K, E537H, E537R, E545K, E545H, and E545R.

In some embodiments, the modified recombinant enzyme comprises a combination of modifications listed in Table 7.

In some embodiments, the amino acid sequence of the modified recombinant enzyme comprises a modification at positions corresponding to E142, 1148, D189, V261, L264, R308, E391, E482, D492, K500, D521, E523, and E537. In some embodiments, the modification at position E142 is E142K; the modification at position 1148 is I148K; the modification at position D 189 is D189K; the modification at position V261 is V261A; the modification at position L264 is L264H; the modification at position R308 is R308G; the modification at position E391 is E391Y; the modification at position E482 is E482K; the modification at position D492 is D492H; the modification at position K500 is K500E; the modification at position D521 is D521K; the modification at position E523 is E523K; and the modification at position E537 is E537K. In some embodiments, the modified recombinant enzyme comprises the amino acid sequence of SEQ ID NO: 88.

In some embodiments, the amino acid sequence of the modified recombinant enzyme comprises a modification at position E60. In some embodiments, the modification at E60 is E60L. In some embodiments, the modified recombinant enzyme comprises the amino acid sequence of SEQ ID NO: 157.

In some embodiments, the modified recombinant enzyme further comprises a bis-biotin tag.

In some embodiments, the modified recombinant enzyme comprises the amino acid sequence of SEQ ID NO: 180.

In some aspects, the disclosure relates to modified recombinant enzymes comprising one or more segments selected from: a first segment having an amino acid sequence that is at least 80%, 80-90%, 90-95%, or at least 95% identical to amino acids 1-196 of SEQ ID NO: 2, wherein the amino acid sequence of the first segment comprises a modification at one or more positions corresponding to K4, T13, S22, V25, C26, D27, N33, 134, F36, S42, D54, N59, E60, E65, E85, M95, N106, T110, T114, K119, Q122, Y133, P136, E139, E142, N145, P147, 1148, E152, 1153, P160, D167, D171, N175, F188, and D189 of SEQ ID NO: 2; a second segment having an amino acid sequence that is at least 80%, 80-90%, 90-95%, or at least 95% identical to amino acids 197- 271 of SEQ ID NO: 2, wherein the amino acid sequence of the second segment comprises a modification at one or more positions corresponding to Q206, T211, S216, R217, D232, A236, V247, 1253, V261, L264, and S267 of SEQ ID NO: 2; and/or a third segment having an amino acid sequence that is at least 80%, 80-90%, 90-95%, or at least 95% identical to amino acids 443- 528 of SEQ ID NO: 2, wherein the amino acid sequence of the third segment comprises a modification at one or more positions corresponding to V443, L445, A446, S447, V449, T450, W452, G453, Y455, F465, N467, T479, E482, A484, E485, A486, L490, D492, S493, K495, K500, S503, Q506, Q513, E519, D521, E523, and V526 of SEQ ID NO: 2.

In some embodiments, the modified recombinant enzyme comprises the first segment and the second segment. In some embodiments, the modified recombinant enzyme comprises the second segment and the third segment. In some embodiments, the modified recombinant enzyme comprises the first segment and the third segment. In some embodiments, the modified recombinant enzyme comprises the first segment, the second segment and the third segment.

In some embodiments, a modification is an amino acid substitution selected from the group consisting of K4R, T13N, S22A, V25L, C26W, D27E, N33T, I34V, F36V, S42T, D54Y, N59D, E60L, E60V, E65S, E85P, M95T, M95K, N106G, T110I, T114S, K119Q, Q122V, Y133L, P136T, E139K, E139Q, E139R, E139H, E142K, E142Q, E142R, E142H, N145K, N145H, N145R, P147Q, P147T, I148K, I148H, I148R, E152D, I153V, P160A, D167P, D167K, D167H, D167R, D171K, D171H, D171R, N175T, N175Y, F188C, D189K, D189H, D189R, Q206R, Q206K, Q206H, T211A, S216G, S216R, R217G, D232K, A236G, V247D, I253H, I253A, V261A, V261I, V261L, L264H, L264A, L264M, S267A, V443T, L445M, A446G, S447V, V449I, T450A, W452Y, G453A, Y455W, F465Y, N467R, N467K, N467H, N467S, N467T, T479V, E482K, E482H, E482R, A484E, E485D, A486E, L490M, D492H, D492K, D492R, D492A, H492S, S493P, K495R, K500E, S503A, S503T, Q506K, Q513D, D521K, D521R, D521H, E523R, E523V, E523Y, E523F, E523H, E523W, and V526L.

In some embodiments, the amino acid sequence of the modified recombinant enzyme comprises a modification at one or more positions corresponding to E139, E142, N145, 1148, D167, D171, D189, N467, E482, D492, K495, D521, and E523. In some embodiments, a modification is an amino acid substitution selected from the group consisting of E139K, E139Q, E139R, E139H, E142K, E142H, E142R, E142Q, N145K, N145H, N145R, I148K, I148H, I148R, D167P, D167K, D167H, D167R, D171K, D171H, D171R, D189K, D189H, D189R, N467R, N467K, N467H, N467S, N467T, E482K, E482H, E482R, D492H, D492K, D492R, K495R, D521K, D521H, D521R, E523K, E523Y, E523H, E523R, E523F, and E523W.

In some embodiments, the amino acid sequence of the modified recombinant enzyme comprises a modification at one or more positions corresponding to P273, P275, R308, V315, Q317, S319, L320, 1322, Q323, D337, E338, D341, T345, F352, F353, T364, D374, 1384, E385, N388, E391, A396, N397, G400, D414, D425, R429, E436, L437, D533, R534, E537, G547, E545, L555, P556, R558, T559, V564, T568, M569, and T571 of SEQ ID NO: 2. In some embodiments, a modification is an amino acid substitution selected from the group consisting of P273S, P273R, P275S, E283K, V315L, S319R, R308G, G308R, Q317R, S319R, L320M,

L320T, I322K, Q323G, Q323V, Q323R, D337G, E338K, D341T, T345I, F352I, F353C, T364I, D374G, D374Q, D374H, I384T, I384F, I384S, E385Y, E385K, E385R, E385N, E385Q, E385L, E385A,, N388T, E391Y, E391W, E391F, E391H, E391M, E391K, E391R, A396Q, N397L, G400L, D414V, D425N, R429G, E436R, E436G, L437Y, L437E, D533A, D533Q, D533T, D533R, D533S, R534K, E537K, E537H, E537R, E545K, E545H, E545R, G547S, L555K, L555R, P556A, R558H, T559V, V564L, T568D, T568S, M569K, M569T, M569V, and T571S. In some embodiments, a modification is an amino acid substitution selected from the group consisting of D374G, D374Q, D374H, E385Y, E385K, E385R, E385N, E385Q, E385L, E385A, E391Y, E391W, E391K, E391F, D533A, D533Q, D533T, D533R, D533S, E537K, E537H, E537R, E545K, E545H, and E545R.

In some embodiments, the modified recombinant enzyme comprises a combination of modifications listed in Table 7.

In some embodiments, the amino acid sequence of the modified recombinant enzyme comprises a modification at positions corresponding to E142, 1148, D189, V261, L264, R308, E391, E482, D492, K500, D521, E523, and E537. In some embodiments, the modification at position E142 is E142K; the modification at position 1148 is I148K; the modification at position D 189 is D189K; the modification at position V261 is V261A; the modification at position L264 is L264H; the modification at position R308 is R308G; the modification at position E391 is E391Y; the modification at position E482 is E482K; the modification at position D492 is D492H; the modification at position K500 is K500E; the modification at position D521 is D521K; the modification at position E523 is E523K; and the modification at position E537 is E537K.

In some embodiments, the modified recombinant enzyme comprises the amino acid sequence of SEQ ID NO: 88.

In some embodiments, the amino acid sequence of the modified recombinant enzyme comprises a modification at position E60. In some embodiments, the modification at E60 is E60L.

In some embodiments, the modified recombinant enzyme comprises the amino acid sequence of SEQ ID NO: 157.

In some embodiments, the modified recombinant enzyme further comprises a bis-biotin tag.

In some embodiments, the modified recombinant enzyme comprises the amino acid sequence of SEQ ID NO: 180.

In some aspects, the disclosure relates to modified recombinant enzymes comprising an amino acid sequence comprising: (i) a first segment, a second segment, a third segment, a fourth segment, a fifth segment, a sixth segment, and a seventh segment; and (ii) a modification at one or more positions corresponding to E139, E142, N145, 1148, D167, D171, D189, D374, E385, E391, N467, E482, D492, K495, D521, E523, D533, E537, and E545 of SEQ ID NO: 2; wherein the first segment comprises an amino acid sequence that is at least 80%, 80-90%, 90-95%, or at least 95% identical to a exonuclease region of a polymerizing enzyme of Table 1, Table 2, or Table 3; the second segment and the sixth segment collectively comprise an amino acid sequence that is at least 80%, 80-90%, 90-95%, or at least 95% identical to a palm region of a

polymerizing enzyme of Table 1, Table 2, or Table 3; the third segment comprises an amino acid sequence that is at least 80%, 80-90%, 90-95%, or at least 95% identical to a TPR1 region of a polymerizing enzyme of Table 1, Table 2, or Table 3; the fourth segment comprises an amino acid sequence that is at least 80%, 80-90%, 90-95%, or at least 95% identical to a finger region of a polymerizing enzyme of Table 1, Table 2, or Table 3; the fifth segment comprises an amino acid sequence that is at least 80%, 80-90%, 90-95%, or at least 95% identical to a TPR2 region of a polymerizing enzyme of Table 1, Table 2, or Table 3; and the seventh segment comprises an amino acid sequence that is at least 80%, 80-90%, 90-95%, or at least 95% identical to a thumb region of a polymerizing enzyme of Table 1, Table 2, or Table 3. In particular embodiments, a polymerizing enzyme from Table 1 is selected from any one of SEQ ID Nos: 2-5. In some embodiments, a polymerizing enzyme from Table 1 is selected from any one of SEQ ID Nos: 23- 33.

In some embodiments, a modification is an amino acid substitution selected from the group consisting of E139K, E139Q, E139R, E139H, E142K, E142H, E142R, E142Q, N145K, N145H, N145R, I148K, I148H, I148R, D167P, D167K, D167H, D167R, D171K, D171H, D171R, D189K, D189H, D189R, D374G, D374Q, D374H, E385Y, E385K, E385R, E385N, E385Q, E385L, E385A, E391Y, E391W, E391K, E391F, N467R, N467K, N467H, N467S, N467T, E482K, E482H, E482R, D492H, D492K, D492R, K495R, D521K, D521H, D521R, E523K, E523Y, E523H, E523R, E523F, E523W, D533A, D533Q, D533T, D533R, D533S, E537K, E537H, E537R, E545K, E545H, and E545R. In some embodiments, the modified recombinant enzyme further comprises a modification at one or more positions corresponding to K4, T13, S22, V25, C26, D27, N33, 134, F36, S42, D54, N59, E60, E65, E85, M95, N106, T110, T114, K119, Q122, Y133, P136, P147, E152, 1153, P160, N175, F188, Q206, T211, S216, R217, D232, A236, V247, 1253, V261, L264, S267, P273, P275, R308, V315, Q317, S319, L320, 1322, Q323, D337, E338, D341, T345, F352, F353, T364, 1384, N388, A396, N397, G400, D414, D425, R429, E436, L437, V443, L445, A446, S447, V449, T450, W452, G453, Y455, F465, T479, A484, E485, A486, L490, S493, K500, S503, Q506, Q513, E519, V526, R534, G547, L555, P556, R558, T559, V564, T568, M569, and T571 of SEQ ID NO: 2. In some

embodiments, a modification is an amino acid substitution selected from the group consisting of K4R, T13N, S22A, V25L, C26W, D27E, N33T, I34V, F36V, S42T, D54Y, N59D, E60L, E60V, E65S, E85P, M95T, M95K, N106G, T110I, T114S, K119Q, Q122V, Y133L, P136T, P147Q, P147T, E152D, I153V, P160A, N175T, N175Y, F188C, Q206R, Q206K, Q206H, T211A, S216G, S216R, R217G, D232K, A236G, V247D, I253H, I253A, V261A, V261I, V261L,

L264H, L264A, L264M, S267A, P273S, P273R, P275S, E283K, V315L, S319R, R308G,

G308R, Q317R, S319R, L320M, L320T, I322K, Q323G, Q323V, Q323R, D337G, E338K, D341T, T345I, F352I, F353C, T364I, I384T, I384F, I384S, N388T, A396Q, N397L, G400L, D414V, D425N, R429G, E436R, E436G, L437Y, L437E, V443T, L445M, A446G, S447V, V449I, T450A, W452Y, G453A, Y455W, F465Y, T479V, A484E, E485D, A486E, L490M, S493P, K500E, S503A, S503T, Q506K, Q513D, V526L, R534K, G547S, L555K, L555R, P556A, R558H, T559V, V564L, T568D, T568S, M569K, M569T, M569V, and T571S. In some embodiments, the modified recombinant enzyme comprises a combination of modifications listed in Table 7.

In some aspects, the disclosure relates to modified recombinant enzymes comprising: an amino acid sequence this is at least 60%, 60-70%, 70-80%, or at least 80% identical to SEQ ID NO: 2; and an extended palm domain, wherein the extended palm domain comprises an addition of an amino acid sequence that is at least 80%, 80-90%, 90-95%, or at least 95% identical to amino acids 505-524 of SEQ ID NO: 1.

In some embodiments, the modified recombinant enzyme further comprises a

modification at one or more positions corresponding to K4, T13, S22, V25, C26, D27, N33, 134, F36, S42, D54, N59, E60, E65, E85, M95, N106, T110, T114, K119, Q122, Y133, P136, E139, E142, N145, N145H, N145R, P147, 1148, E152, 1153, P160, D167, D171, N175, F188, D189, Q206, T211, S216, R217, D232, A236, V247, 1253, V261, L264, S267, V443, L445, A446, S447, V449, T450, W452, G453, Y455, F465, N467, T479, E482, A484, E485, A486, L490, D492, S493, K495, K500, S503, Q506, Q513, E519, D521, E523, and V526 of SEQ ID NO: 2. In some embodiments, a modification is an amino acid substitution selected from the group consisting of K4R, T13N, S22A, V25L, C26W, D27E, N33T, I34V, F36V, S42T, D54Y, N59D, E60L, E60V, E65S, E85P, M95T, M95K, N106G, T110I, T114S, K119Q, Q122V, Y133L, P136T, E139K, E139Q, E139R, E139H, E142K, E142Q, E142R, E142H, N145K, N145H, N145R, P147Q, P147T, I148K, I148H, I148R, E152D, I153V, P160A, D167P, D167K, D167H, D167R, D171K, D171H, D171R, N175T, N175Y, F188C, D189K, D189H, D189R, Q206R, Q206K, Q206H, T211A, S216G, S216R, R217G, D232K, A236G, V247D, I253H, I253A, V261A, V261I, V261L, L264H, L264A, L264M, S267A, V443T, L445M, A446G, S447V, V449I, T450A, W452Y, G453A, Y455W, F465Y, N467R, N467K, N467H, N467S, N467T, T479V, E482K, E482H, E482R, A484E, E485D, A486E, L490M, D492H, D492K, D492R, D492A, H492S, S493P, K495R, K500E, S503A, S503T, Q506K, Q513D, D521K, D521R, D521H, E523R, E523V, E523Y, E523F, E523H, E523W, and V526L. In some embodiments, the amino acid sequence of the modified recombinant enzyme further comprises a modification at one or more positions corresponding to E139, E142, N145, 1148, D167, D171, D189, N467, E482, D492, K495, D521, and E523. In some embodiments, a modification is an amino acid substitution selected from the group consisting of E139K, E139Q, E139R, E139H, E142K, E142H, E142R, E142Q, N145K, N145H, N145R, I148K, I148H, I148R, D167P, D167K, D167H, D167R, D171K, D171H, D171R, D189K, D189H, D189R, N467R, N467K, N467H, N467S, N467T, E482K, E482H, E482R, D492H, D492K, D492R, K495R, D521K, D521H, D521R, E523K, E523Y, E523H, E523R, E523F, and E523W. In some embodiments, the amino acid sequence of the modified recombinant enzyme comprises a modification at one or more positions corresponding to P273, P275, R308, V315, Q317, S319, L320, 1322, Q323, D337, E338, D341, T345, F352, F353, T364, D374, 1384, E385, N388, E391, A396, N397, G400, D414, D425, R429, E436, F437, D533, R534, E537, G547, E545, F555, P556, R558, T559, V564, T568, M569, and T571 of SEQ ID NO: 2. In some embodiments, a modification is an amino acid substitution selected from the group consisting of P273S, P273R, P275S, E283K, V315L, S319R, R308G, G308R, Q317R, S319R, L320M,

L320T, I322K, Q323G, Q323V, Q323R, D337G, E338K, D341T, T345I, F352I, F353C, T364I, D374G, D374Q, D374H, I384T, I384F, I384S, E385Y, E385K, E385R, E385N, E385Q, E385L, E385A, N388T, E391Y, E391W, E391F, E391H, E391M, E391K, E391R, A396Q, N397L, G400L, D414V, D425N, R429G, E436R, E436G, L437Y, L437E, D533A, D533Q, D533T, D533R, D533S, R534K, E537K, E537H, E537R, E545K, E545H, E545R, G547S, L555K, L555R, P556A, R558H, T559V, V564L, T568D, T568S, M569K, M569T, M569V, and T571S. In some embodiments, a modification is an amino acid substitution selected from the group consisting of D374G, D374Q, D374H, E385Y, E385K, E385R, E385N, E385Q, E385L, E385A, E391Y, E391W, E391K, E391F, D533A, D533Q, D533T, D533R, D533S, E537K, E537H, E537R, E545K, E545H, and E545R.

In some embodiments, the modified recombinant enzyme comprises a combination of modifications listed in Table 7.

In some aspects, the disclosure relates to modified recombinant enzymes having an amino acid sequence that is at least 60%, 60-70%, 70-80%, or at least 80% identical to any one of SEQ ID NOs: 1-33, wherein the amino acid sequence comprises a modification at one or more positions corresponding to K4, T13, S22, V25, C26, D27, N33, 134, F36, S42, D54, N59, E60, E65, E85, M95, N106, T110, T114, K119, Q122, Y133, P136, E139, E142, N145, P147, 1148, E152, 1153, PI 60, D167, D171, N175, F188, D189, Q206, T211, S216, R217, D232, A236, V247, 1253, V261, L264, S267, P273, P275, R308, V315, Q317, S319, L320, 1322, Q323, D337, E338, D341, T345, F352, F353, T364, D374, 1384, E385, N388, E391, A396, N397, G400,

D414, D425, R429, E436, L437, V443, L445, A446, S447, V449, T450, W452, G453, Y455, F465, N467, T479, E482, A484, E485, A486, L490, D492, S493, K495, K500, S503, Q506, Q513, E519, D521, E523, V526, D533, R534, E537, G547, E545, L555, P556, R558, T559, V564, T568, M569, and T571 of E. faecium polymerase (SEQ ID NO: 2). In particular embodiments, a modified recombinant enzyme has an amino acid sequence that is at least 60%, 60-70%, 70-80%, or at least 80% identical to any one of SEQ ID NOs: 2-5 and comprises a modification at one or more of the above positions. In a particular embodiment, a modified recombinant enzyme is a modified E. faecium polymerase that has an amino acid sequence that is at least 60%, 60-70%, 70-80%, or at least 80% identical to any one of SEQ ID NO: 2 and comprises a modification at one or more of the above positions. In a particular embodiments, a modified recombinant enzyme is a modified E. faecium polymerase that comprises the amino acid sequence of SEQ ID NO: 2 and comprises a modification at one or more of the positions. In some embodiments, a modified recombinant enzyme has an amino acid sequence that is 60%, 60-70%, 70-80%, or at least 80% identical to any one of SEQ ID NOs: 23-33, and comprises a modification at one or more of the above positions.

In some embodiments, the modified recombinant enzyme comprises a modification at one or both positions corresponding to T568 and M569 of SEQ ID NO: 2. In some embodiments, the modification is an amino acid substitution selected from the group consisting of T568D, T568S, M569T, and M569V. In some embodiments, the modified recombinant enzyme has improved processivity relative to E. faecium polymerase (SEQ ID NO: 2).

In some embodiments, the modified recombinant enzyme comprises a modification at a position corresponding to N59 of SEQ ID NO: 2. In some embodiments, the modification is N59D. In some embodiments, the modified recombinant enzyme has altered exonuclease activity relative to E. faecium polymerase (SEQ ID NO: 2).

In some embodiments, the modified recombinant enzyme comprises a modification at one or more positions corresponding to V261, L264, S267, 1384, E391, W452, G453, Y455, D492, and K500 of SEQ ID NO: 2. In some embodiments, a modification is an amino acid substitution selected from the group consisting of V261A, V261I, L264A, L264H, L264M, S267A, I384F, I384S, E391Y, E391W, E391F, E391H, E391M, E391K, E391R, W452Y, G453A, Y455W, D492H, and K500E. In some embodiments, the modified recombinant enzyme has improved nucleotide substrate utilization relative to E. faecium polymerase (SEQ ID NO: 2).

In some embodiments, the modified recombinant enzyme comprises a modification at one or more positions corresponding to E65, Y133, V261, L264, S267, 1384, E391, G400, V443, L445, A446, S447, V449, T450, W452, G453, Y455, K500, S503, E523, L555, and P556 of SEQ ID NO: 2. In some embodiments, a modification is an amino acid substitution selected from the group consisting of E65S, Y133L, V261A, V261I, L264A, L264H, S267A, I384F, I384S, E391Y, E391W, E391F, E391K, G400L, V443T, L445M, A446G, S447V, V449I,

T450A, W452Y, G453A, Y455W, K500E, S503A, E523K, E523Y, E523F, E523H, E523W, L555K, and P556A. In some embodiments, the modified recombinant enzyme has improved accuracy relative to E. faecium polymerase (SEQ ID NO: 2). In some embodiments, the modified recombinant enzyme comprises a modification at one or more positions corresponding to Q317, S319, 1322, Q323, R429, L555, and T559 of SEQ ID NO: 2. In some embodiments, a modification is an amino acid substitution selected from the group consisting of Q317R, S319R, I322K, Q323G, R429G, L555K, and T559V. In some embodiments, the modified recombinant enzyme has an increased DNA-binding affinity relative to E. faecium polymerase (SEQ ID NO: 2).

In some embodiments, the modified recombinant enzyme comprises a modification at one or more positions corresponding to E391, S503 and E523 of SEQ ID NO: 2. In some

embodiments, a modification is an amino acid substitution selected from the group consisting of E391Y, E391W, E391F, E391K, S503A, E523K, E523Y, E523F, E523H, and E523W. In some embodiments, the modified recombinant enzyme has an increased analog-binding affinity relative to E. faecium polymerase (SEQ ID NO: 2).

In some embodiments, the modified recombinant enzyme comprises a modification at one or more positions corresponding to Q206, E436 and L437 of SEQ ID NO: 2. In some

embodiments, a modification is an amino acid substitution selected from the group consisting of Q206R, Q206K, Q206H, E436R, L437Y, and L437E. In some embodiments, the modified recombinant enzyme has improved strand displacement relative to E. faecium polymerase (SEQ ID NO: 2).

In some embodiments, the modified recombinant enzyme comprises a modification at one or more positions corresponding to E436, L437, R534, T568, and M569 of SEQ ID NO: 2. In some embodiments, a modification is an amino acid substitution selected from the group consisting of E436R, L437Y, L437E, R534K, T568D, T568S, M569T, and M569V. In some embodiments, the modified recombinant enzyme has an enhanced average read length relative to E. faecium polymerase (SEQ ID NO: 2).

In some embodiments, the modified recombinant enzyme comprises a modification at one or more positions corresponding to T13, V25, C26, D27, N33, 134, F36, S42, D54, E60, M95, T110, T114, K119, P136, P147, E152, 1153, P160, N175, F188, S216, R217, D232, A236, V247, P273, P275, E283, V315, S319, L320, Q323, E338, T345, F352, F353, T364, D414, D425,

E436, F465, E485, A486, L490, S503, E523, V526, G547, L555, R558,V564, M569, and T571 of SEQ ID NO: 2. In some embodiments, a modification is an amino acid substitution selected from the group consisting of T13N, V25L, C26W, D27E, N33T, I34V, F36V, S42T, D54Y, E60V, M95T, M95K, T110I, T114S, K119Q, P136T, P147Q, P147T, E152D, I153V, P160A, N175Y, F188C, S216G, S216R, R217G, D232H, A236G, V247D, P273R, P275S, E283K, V315L, S319R, L320M, L320T, Q323R, E338K, T345I, F352I, F353C, T364I, D414V, D425N, E436G, F465Y, E485D, A486E, L490M, S503T, E523V, V526L, G547S, L555R, R558H, V564L, M569K, and T571S. In some embodiments, the modified recombinant enzyme has an increased replication capacity relative to E. faecium polymerase (SEQ ID NO: 2).

In some embodiments, the modified recombinant enzyme comprises a modification at one or more positions corresponding to E139, E142, N145, 1148, D167, D171, D189, D374, E385, E391, N467, E482, D492, K495, D521, E523, D533, E537, and E545 of SEQ ID NO: 2. In some embodiments, a modification is an amino acid substitution selected from the group consisting of E139K, E139Q, E139R, E139H, E142K, E142H, E142R, E142Q, N145K, N145H, N145R, I148K, I148H, I148R, D167P, D167K, D167H, D167R, D171K, D171H, D171R, D189K, D189H, D189R, D374G, D374Q, D374H, E385Y, E385K, E385R, E385N, E385Q, E385L, E385A, E391Y, E391W, E391K, E391F, N467R, N467K, N467H, N467S, N467T, E482K, E482H, E482R, D492H, D492K, D492R, K495R, D521K, D521H, D521R, E523K, E523Y, E523H, E523R, E523F, E523W, D533A, D533Q, D533T, D533R, D533S, E537K, E537H, E537R, E545K, E545H, and E545R. In some embodiments, the modified recombinant enzyme has an increased electropositive surface charge relative to E. faecium polymerase (SEQ ID NO: 2).

In some embodiments, the modified recombinant enzyme comprises a modification at one or more positions corresponding to K4, S22, D27, 134, D54, E60, E85, M95, N106, T110, Q122, Y133, P136, P147, D167, T211, D232, P275, R308, S319, L320, E323, D337, E338, D341,

T345, F352, T364, D414, F465, T479, E485, L490, S493, Q513, and R558 of SEQ ID NO: 2. In some embodiments, a modification is an amino acid substitution selected from the group consisting of K4R, S22A, D27E, I34V, D54Y, E60V, E60L, E85P, M95K, T110I, N106G, Q122V, Y133L, P136T, P147Q, P147T, D167P, T211A, D232K, P275S, R308G, S319R, L320M, Q323V, D337G, E338K, D341T, T345I, F352I, T364I, D414V, F465Y, T479V, E485D, L490M, S493P, Q513D, and R558H. In some embodiments, the modified recombinant enzyme has an increased stability relative to E. faecium polymerase (SEQ ID NO: 2).

In some embodiments, the modified recombinant enzyme comprises a combination of modifications listed in Table 7.

A modified polymerase may include one or more modifications (e.g., a deletion of one or more amino acids, an addition of one or more amino acids, a substitution of one or more amino acids as described in this application, or a combination thereof) relative to a wild-type

polymerase (e.g., a sequence of Table 1, e.g., SEQ ID NO: 1, SEQ ID Nos: 2-5, SEQ ID Nos: 6- 22, or SEQ ID Nos: 23-33), or relative to a sequence described in any of Tables 2-7. In some embodiments, the only modifications in a modified polymerase are one or more of the modifications (e.g., amino acid substitutions) provided in this disclosure and the sequence of the polymerase is otherwise identical to a wild-type polymerase (e.g., a sequence of TABLE 1) or to a sequence described in any of TABLES 2-7.

In some embodiments, a modified recombinant enzyme further comprises a purification tag. In some embodiments, the purification tag is covalently bound to a region within the polymerizing enzyme sequence. In some embodiments, the purification tag is covalently bound at a terminal end of the polymerizing enzyme sequence. In some embodiments, the purification tag is a C-terminal tag. In some embodiments, the purification tag is an N-terminal tag. In some embodiments, the purification tag is a His tag (e.g., a sequence of repeating histidine residues, such as a hexahistidine sequence).

In some embodiments, a modified recombinant enzyme further comprises a coupling group. In some embodiments, the coupling group is attached at a region within the modified recombinant enzyme sequence. In some embodiments, the coupling group is attached at a terminal end of the modified recombinant enzyme. In some embodiments, the coupling group is attached at a C-terminal end of the modified recombinant enzyme. In some embodiments, the coupling group is attached at an N-terminal end of the modified recombinant enzyme. In some embodiments, the coupling group is a biotinylation sequence. In some embodiments, the coupling group is a bis-biotinylation sequence. In some embodiments, a modified recombinant enzyme comprises (e.g., at its C terminus) a purification tag (e.g., a His tag) and a coupling group (e.g., a biotinylation or bis-biotinylation sequence) directly connected or separated by a peptide linker (e.g., 5-15 amino acids long or longer).

In some embodiments, a modified recombinant enzyme is immobilized on a surface. In some embodiments, the surface comprises a coupling group configured to bind the modified recombinant enzyme. In some embodiments, the surface comprises a nanoaperture. In some embodiments, the surface comprises a bottom surface of a sample well. In some embodiments, the sample well is disposed among a plurality of sample wells on a surface (e.g., a surface of a chip or an integrated device). In some embodiments, each of the plurality of sample wells are configured to receive a modified recombinant enzyme. In some embodiments, each of the plurality of sample wells comprising a modified recombinant enzyme are capable of conducting a single molecule sequencing reaction. In some embodiments, the surface can be a surface of a chip made from glass or other transparent material, silica, fused silica, silicon dioxide, a polymer, other material, or a combination thereof (e.g., a combination of different layers, for example including one or more metal layers). In some aspects, the disclosure provides an isolated nucleic acid molecule that encodes a modified recombinant enzyme described herein. In some embodiments, the isolated nucleic acid molecule comprises RNA. In some embodiments, the isolated nucleic acid molecule comprises DNA. In some embodiments, the isolated nucleic acid molecule comprises a viral vector. In some embodiments, the isolated nucleic acid molecule comprises an expression vector. In some embodiments, the isolated nucleic acid molecule comprises a plasmid. In some embodiments, the isolated nucleic acid includes a promoter (e.g., an inducible promoter). In some

embodiments, the isolated nucleic acid is in a host cell capable of expressing the modified recombinant enzyme. In some embodiments, the modified recombinant enzyme is isolated from the host cell (e.g., from a host cell preparation, for example after growth in a bioreactor and induction of an inducible promoter).

In some aspects, the disclosure provides a composition comprising a modified

recombinant enzyme described in this application. In some embodiments, the composition is used in a method of sequencing a nucleic acid. In some embodiments, the composition further comprises a sequencing reaction mixture. In some embodiments, the sequencing reaction mixture can include one or more of a nucleoside polyphosphate (e.g., a nucleoside comprising more than one phosphate group, such as a nucleotide or a nucleoside hexaphosphate), a template nucleic acid to be sequenced, a nucleic acid primer that serves as a starting point for

complementary strand synthesis, a divalent metal ion, a buffer component, and a salt. In some embodiments, the nucleoside polyphosphate comprises a detectable moiety (e.g., a luminescent label).

In some aspects, the disclosure provides a method of sequencing a nucleic acid by contacting a modified recombinant enzyme described in this application with a sequencing reaction mixture. In some embodiments, the sequencing reaction mixture can include one or more of a nucleoside polyphosphate (e.g., a nucleoside comprising more than one phosphate group, such as a nucleotide or a nucleoside hexaphosphate), a template nucleic acid to be sequenced, a nucleic acid primer that serves as a starting point for complementary strand synthesis, a divalent metal ion, a buffer component, and a salt. In some embodiments, the nucleoside polyphosphate comprises a luminescent label. In some embodiments, the method further comprises detecting incorporation of one or more nucleoside polyphosphates in a growing strand complementary to the template nucleic acid. In some embodiments, detecting comprises measuring one or more luminescent properties (e.g., lifetime, intensity, photon arrival time, quantum yield) of a luminescently labeled nucleoside polyphosphate involved in an

incorporation event. In some aspects, the disclosure relates to compositions comprising a modified recombinant enzyme described herein.

In some aspects, the disclosure relates to methods of sequencing a nucleic acid using a recombinant enzyme described herein. In some embodiments, the method comprises contacting the modified recombinant enzyme with a sequencing reaction mixture.

These and other aspects are described in more detail in the following detailed description and illustrated by the non-limiting drawings and examples.

BRIEF DESCRIPTION OF THE DRAWINGS

The skilled artisan will understand that the figures, described herein, are for illustration purposes only. It is to be understood that, in some instances, various aspects of the invention may be shown exaggerated or enlarged to facilitate an understanding of the invention. In the drawings, like reference characters generally refer to like features, functionally similar and/or structurally similar elements throughout the various figures. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the teachings. The drawings are not intended to limit the scope of the present teachings in any way.

The features and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings.

When describing embodiments in reference to the drawings, direction references (“above,”“below,”“top,”“bottom,”“left,”� ��right,”“horizontal,”“vertical,” etc.) may be used. Such references are intended merely as an aid to the reader viewing the drawings in a normal orientation. These directional references are not intended to describe a preferred or only orientation of an embodied device. A device may be embodied in other orientations.

As is apparent from the detailed description, the examples depicted in the figures and further described for the purpose of illustration throughout the application describe non-limiting embodiments, and in some cases may simplify certain processes or omit features or steps for the purpose of clearer illustration.

FIG. 1 is a schematic that illustrates the progression of a polymerization reaction in relation to signal readout in a non-limiting process for monitoring single molecule processes.

FIG. 2 is a non-limiting illustration that depicts the structure of F29 polymerase and domains and subdomains of the polymerase.

FIG. 3 depicts non-limiting examples of selected mutational variants with sites of mutation within domains and subdomains of polypeptide strands. FIG. 4 depicts non-limiting examples of selected chimeric polymerase variants having different domains and subdomains substituted into the polypeptide strands.

FIG. 5A is a non-limiting illustration that depicts a loop region in an exonuclease domain of F29 polymerase.

FIG. 5B depicts a sequence homology alignment between exonuclease regions of F29 polymerase and a non-limiting set of other polymerases.

FIG. 6 depicts non-limiting generic examples of chimeric polymerase variants comprising one or more site-specific mutations.

FIG. 7 is a picture of an SDS-PAGE conducted to evaluate purity of polymerases expressed in E. coli.

FIGs. 8A-8D show results from DNA synthesis experiments with E. faecium polymerase variants, EFM37, EFM48, and EFM66. FIG. 8A depicts sequencing chips loaded with EFM37- dumbbell ternary complexes. FIG. 8B illustrates a real-time stopped-flow strand-displacement DNA synthesis assay. FIG. 8C shows DNA synthesis rates determined for the different variants. FIG. 8D shows amplitudes determined for the different variants.

FIGs. 9A-9B show a structural characterization of wild-type E. faecium polymerase.

FIG. 9A shows a modeled surface of wild-type E. faecium polymerase. FIG. 9B shows polymerase homology domains mapped to the wild-type E. faecium polypeptide.

FIGs. 10A-10F show results from DNA synthesis experiments with E. faecium polymerase variants developed based on the EFM37 parent. FIG. 10A shows DNA synthesis rates determined for different variants in stopped-flow strand displacement synthesis assays with dN6P analogs and analogs containing duplex DNA linkers (“Q24”). FIG. 10B is a plot showing the number of negatively and positively charged residues in wild-type and variant polymerases. FIG. IOC depicts modeled electrostatic surfaces of wild-type and variant polymerases. FIGs. 10D-10E show improvements in EFM89 rate (FIG. 10D) and amplitude (FIG. 10E) with 25mM vs lOmM MgC12 in stopped-flow strand-displacement synthesis assays with Q24s. FIG. 10F shows amplitude of DNA synthesis using dNTP in stopped-flow strand displacement synthesis assays for wild-type EF, EF exo-, and EFM89 at 30°C and 25 mM MgC12.

FIG. 11 shows an example sequencing alignment obtained from a sequencing reaction using EFM89 and M13 ssDNA plasmid template.

FIGs. 12A-12D shows results from DNA sequencing reactions on a commercial platform with two independent preparations of EFM89. FIG 12A reports various output measurements. FIG. 12B shows boxplots indicating the distribution of insertion, deletion, and mismatch errors with EFM89, with average values indicated above each boxplot. FIG. 12C shows a histogram of total read length for EFM89 (batch 1). FIG. 12D shows a histogram of subread accuracy for EFM89 (batch 1).

FIGs. 13A-13B show sequence alignment results. FIG. 13A shows sequence identity between four naturally occurring E. faecium polymerase variants. FIG. 13B shows sequences identity shared between the variants. Sequences are listed by their NCBI protein database accession numbers.

FIGs. 14A-14B show comparisons of E. faecium polymerase and F29. FIG.14A shows an amino acid sequence alignment of the N-terminal ends of E. faecium polymerase and F29. FIG. 14B shows a crystal structure comparisons of the E. faecium polymerase and F29 fingers subdomain (top) and palm subdomain (bottom). F29 has an extended structure in the palm domain, which may be included in an E. faecium polymerase, for example, to provide favorable interactions with nucleotide analogs (e.g., dN6P utilization) and to provide a structural feature with closer proximity to the fingers domain when nucleotide analogs are bound.

FIG. 15 shows domain organization of E. faecium polymerase relative to F29, with start positions of each domain indicated.

FIG. 16 is a picture of an SDS-PAGE conducted to evaluate purity of the indicated polymerases.

FIG. 17 show an amino acid sequence alignment of the sequence of E. faecium polymerase and seventeen homologous polymerase. Sequences from top to bottom are:

WP_060797276.1 (SEQ ID NO: 2); NP_690635.1 (SEQ ID NO: 828); YP_002004529.1 (SEQ ID NO: 829); KNC25437.1 (SEQ ID NO: 830); NP_073685.1 (SEQ ID NO: 10); ARM70154.1 (SEQ ID NO: 22); ARQ95230.1 (SEQ ID NO: 831); QDH50332.1 (SEQ ID NO: 832);

HMB70020.1 (SEQ ID NO: 833); YP_009198012.1 (SEQ ID NO: 9); WP_077841611.1 (SEQ ID NO: 834); PWM80583.1 (SEQ ID NO: 835); PWM70763.1 (SEQ ID NO: 836);

YP_001333659.1 (SEQ ID NO: 11); KKP77830.1 (SEQ ID NO: 12); AYQ98978.1 (SEQ ID NO: 837); AYQ99922.1 (SEQ ID NO: 838); and AXF52067.1 (SEQ ID NO: 839). Various positions are highlighted (with asterisks), including E60 (substitution L), E139 (substitutions K, Q, T, A, V) and D167 (substitutions P, K, S, Q, A).

FIG. 18 shows the region surrounding residue 60 in an in-house crystal structure of wild- type E. faecium polymerase compared with the same region in F29 polymerase.

FIG. 19 shows results from DNA sequencing reactions with preparations of EFM89 and EFM158.

FIG. 20 shows read lengths achieved using EFM89 polymerase (left) and EFM158 polymerase (right). FIG. 21 shows crystal structure comparisons of wild-type E. faecium polymerase and EFM158, including a view of active site (left) and a view of the surface of the evolved variant (right).

FIGs. 22A-22C shows decreased interpulse duration with introduction of positively charged amino acids at positions 1148 (FIG. 22A), E482 (FIG. 22B) and D492 (FIG. 22C).

Interpulse durations from single-molecule DNA sequencing are displayed for a pair of E. faecium polymerase variants that differ in sequence only at the position noted. Interpulse duration decreased by 21.3%, 5.8%, and 22.6% for I148K, E482K, and D492H, respectively.

FIG. 23 shows single substitutions and combinations that improve alignment accuracy in single molecule DNA sequencing. Variant sequence identifiers are listed in parentheses. All variants have amino acid sequences that are equivalent to EFM182 except at the positions noted. Substitutions are written with respect to EFM182.

FIG. 24 shows results from rolling-circle assays assessing the processivity of wild-type EF polymerase carried out for 30 min at 30°C with a 90-mer dumbbell DNA template with dNTPs (left) and dN6P analogs (right). Results with known processive polymerase QTDE1.0 are shown as a reference.

FIG. 25 shows substitutions enriched in an emulsion-based IVTT-RCA screen with E. faecium polymerase.

DETAILED DESCRIPTION

Aspects of the disclosure relate to modified polymerizing enzymes and compositions thereof. In some aspects, the disclosure provides methods of using modified recombinant polymerizing enzymes and compositions comprising the enzymes. In some embodiments, the disclosure provides modified recombinant polymerizing enzymes and compositions which may be used for conducting in vitro polymerization reactions. In some aspects, the polymerizing enzymes described herein are modified recombinant nucleic acid polymerases, e.g., modified recombinant DNA polymerases. In some embodiments, modified recombinant DNA

polymerases provided by the disclosure may be used for in vitro reactions related to the manipulation of DNA (e.g., DNA sequencing).

I. Modified Polymerizing Enzymes

Among other aspects, the disclosure provides modified polymerizing enzymes (or modified polymerases) that may be used to conduct in vitro polymerization reactions. In some embodiments, polymerases described herein comprise one or more modifications which— individually or in combination— are useful to conduct a sequencing reaction. In some embodiments, one or more of the modifications described herein can be utilized to produce a polymerase having one or more properties useful for conducting sequencing reactions, e.g., properties such as polymerase processivity, fidelity (e.g., accuracy), substrate (e.g., nucleoside polyphosphate) binding affinity, substrate utilization (e.g., the rate at which nucleoside polyphosphates are incorporated into a growing strand complementary to a template strand), polymerase interactions with modified substrates (e.g., labeled nucleoside polyphosphates), or some combination thereof. In some embodiments, one or more of the modifications minimize or eliminate proofreading capability of the polymerase. For example, in some embodiments, one or more modifications may be made to an exonuclease domain of a polymerase that effects a loss in exonuclease activity of the polymerase.

The present application is based in part on the recognition by the inventors that certain modifications (e.g., mutations, insertions, and/or substitutions) to wild-type polymerases enhance functional attributes of said polymerases to provide improved reagents for nucleic acid manipulation applications. As such, in some aspects, the disclosure relates to modified polymerizing enzymes. The terms“polymerase” or“polymerizing enzyme” as used herein, generally refer to any enzyme capable of catalyzing a polymerization reaction. Examples of polymerases include, but are not limited to, a DNA polymerase, an RNA polymerase, a thermostable polymerase, a wild-type polymerase, a recombinant polymerizing enzyme, Escherichia coli DNA polymerase I, T7 DNA polymerase, bacteriophage T4 DNA polymerase cp29 (phi29) DNA polymerase, Taq polymerase, Tth polymerase, Tli polymerase, Pfu

polymerase, Pwo polymerase, VENT® polymerase, Deep VENT™ polymerase, Ex TAQ™ polymerase, LA TAQ™ polymerase, Sso polymerase, Poc polymerase, Pab polymerase, Mth polymerase, ES4 polymerase, Tru polymerase, Tac polymerase, Tne polymerase, Tma polymerase, Tea polymerase, Tih polymerase, Tfi polymerase, PLATINUM® Taq polymerases, Tbr polymerase, Tfl polymerase, Tth polymerase, PFUTURBO® polymerase, PYROBEST™ polymerase, Pwo polymerase, KOD polymerase, Bst polymerase, Sac polymerase, Klenow fragment, polymerase with 3' to 5' exonuclease activity, and variants, modified products and derivatives thereof. In some embodiments, the polymerase is a single subunit polymerase.

Additional example of polymerases include M2Y polymerase, Lucilia cuprina polymerase, Enterococcus faecium polymerase, Bacillus phage VMY22 polymerase, Bacillus phage GA-1 polymerase, Actinomyces phage AV-1 polymerase, Candidatus Moranbacteria polymerase, Bacillus phage MG-B 1 polymerase, Eggerthella sp. polymerase, Streptococcus phage CP-7 polymerase, Bacteroides sp. polymerase, Chlamydia trachomatis polymerase, and Globodera pallida polymerase. Further non-limiting examples of DNA polymerases include 9°NM™ DNA polymerase (New England Biolabs), and a P680G mutant of the Klenow exo- polymerase (Tuske et al. (2000) JBC 275(31):23759-23768). Non-limiting examples of DNA polymerases and their properties are described in detail in, among other places, DNA Replication 2nd edition, Komberg and Baker, W. H. Freeman, New York, N.Y. (1991). Non-limiting examples of such sequences can be found in TABLE 1.

As described herein, polymerases and/or polymerase sequences are“homologous” when they are derived, naturally or artificially, from a common ancestral protein or amino acid sequence. Similarly, nucleic acids and/or nucleic acid sequences are homologous when they are derived, naturally or artificially, from a common ancestral nucleic acid or nucleic acid sequence. For example, any naturally occurring nucleic acid can be modified by any available mutagenesis method to include at least one specific codon that encodes for an amino acid that does not naturally occur at a given position in the polypeptide. When expressed, this mutagenized nucleic acid encodes a polypeptide comprising one or more mutated amino acids. In some embodiments, homology is generally inferred from sequence similarity between two or more nucleic acids or proteins (or sequences thereof). The precise percentage of similarity between sequences that is useful in establishing homology varies with the nucleic acid and protein at issue, but as little as 25% sequence similarity is routinely used to establish homology. Higher levels of sequence similarity, e.g., 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95% or 99% or more can also be used to establish homology. Methods for determining sequence similarity percentages are well known to those having ordinary skill in the art. In some embodiments, similarity can be determined using algorithms such as those described herein, including for example BLASTP and BLASTN algorithms, for example, using default parameters.

TABLE 1. Exemplary Wild-Type Polymerase Amino Acid Sequences

Polymerases have various characteristics, including processivity. Polymerase processivity generally refers to the capability of a polymerase to consecutively incorporate dNTPs into a nucleic acid template without releasing the nucleic acid template. Upon base pairing between a nucleobase of a target nucleic acid and the complementary dNTP, the polymerase incorporates the dNTP into the newly synthesized nucleic acid strand by forming a phosphodiester bond between the 3' hydroxyl end of the newly synthesized strand and the alpha phosphate of the dNTP. Processivity is measured by the average number of nucleotides incorporated by a polymerase on a single association/disassociation event.

The processivity of polymerases vary. For example, a polymerase may exhibit high processivity relative to another polymerase. Alternatively, a polymerase may exhibit reduced processivity relative to another polymerase. Similarly, a polymerase may exhibit high

processivity in a first condition (e.g., comprising a first combination of nucleotides) and reduced processivity in a second condition (e.g., comprising a second combination of nucleotides).

Additional characteristics of polymerases include, but are not limited to, synthesis accuracy, nuclease activity, nucleotide substrate utilization, nucleic acid affinity, replication capacity, average read length production, surface charge, and stability. Similar to processivity, these characteristics vary between polymerases and between reaction conditions.

The characteristics of a polymerase may be altered by the introduction of modifications (or changes) in the amino acid sequence of the polymerase. For example, in some embodiments, the processivity of a polymerase is increased (or, alternatively decreased) by modification. In some embodiments, the nuclease activity of a polymerase is increased (or, alternatively decreased) by modification. In some embodiments, the nucleotide substrate utilization (of one or more substrates) of a polymerase is increased (or, alternatively decreased) by modification. In some embodiments, the affinity of a polymerase toward one more substrates is increased (or, alternatively decreased) by modification. In some embodiments, the replication capacity of a polymerase is increased (or, alternatively decreased) by modification. In some embodiments, the average read length of a polymerase is increased (or, alternatively decreased) by modification. In some embodiments, the surface charge of a polymerase is made more positive (or, alternatively more negative) by modification. In some embodiments, the stability of a polymerase is increased (or, alternatively decreased) by modification. In some embodiments, one or more characteristics of a polymerase (e.g., processivity, nuclease activity, nucleotide substrate utilization, affinity toward one or more substrates, replication capacity, average read length, surface charge, stability, etc.) are increased by about 5%-10%, 10%-20%, 20%-30%, 30%-40%, 40%-50%, 50%-60%, 60%-70%, 70%-80%, 80%-90%, 90%-100%, or more. In some embodiments, one or more characteristics of a polymerase (e.g., processivity, nuclease activity, nucleotide substrate utilization, affinity toward one or more substrates, replication capacity, average read length, surface charge, stability, etc.) are increased by more than about 5%, by more than about 10%, by more than about 20%, by more than about 30%, by more than about 40%, by more than about 50%, by more than about 60%, by more than about 70%, by more than about 80%, by more than about 90%, by more than about 100%, or more. In some embodiments, one or more

characteristics of a polymerase (e.g., processivity, nuclease activity, nucleotide substrate utilization, affinity toward one or more substrates, replication capacity, average read length, surface charge, stability, etc.) are decreased by about 5%-10%, 10%-20%, 20%-30%, 30%-40%, 40%-50%, 50%-60%, 60%-70%, 70%-80%, 80%-90%, 90%-100%, or more. In some embodiments, one or more characteristics of a polymerase (e.g., processivity, nuclease activity, nucleotide substrate utilization, affinity toward one or more substrates, replication capacity, average read length, surface charge, stability, etc.) are decreased by more than about 5%, by more than about 10%, by more than about 20%, by more than about 30%, by more than about 40%, by more than about 50%, by more than about 60%, by more than about 70%, by more than about 80%, or by more than about 90%. In some embodiments, one or more characteristics may be eliminated.

When a modification is introduced into the amino acid sequence of a polymerase, a “modified polymerase” (also referred to herein as a“modified polymerizing enzyme” or, when produced recombinantly, a“modified recombinant polymerase”) is produced. A modification may comprise a deletion of one or more amino acids, an addition of one or more amino acids, a substitution of one or more amino acids, or a combination thereof. A modified polymerase may include one or more modifications (e.g., a deletion of one or more amino acids, an addition of one or more amino acids, a substitution of one or more amino acids as described in this application, or a combination thereof) relative to a wild-type polymerase (e.g., a sequence of Table 1, e.g., SEQ ID NO: 1, SEQ ID Nos: 2-5, SEQ ID Nos: 6-22, or SEQ ID Nos: 23-33), or relative to a sequence described in any of Tables 2-7. For example in some embodiments, a modification comprises a deletion, addition, or substitution of at least 1, at least 2, at least 3, at least 4, at least 5, at least 6, at least 7, at least 8, at least 9, at least 10, at least 11, at least 12, at least 13, at least 14, at least 15, at least 16, at least 17, at least 18, at least 19, at least 20, at least 21, at least 22, at least 23, at least 24, at least 25, at least 26, at least 27, at least 28, at least 29, at least 30, at least 31, at least 32, at least 33, at least 34, at least 35, at least 36, at least 37, at least 38, at least 39, at least 40, at least 41, at least 42, at least 43, at least 44, at least 45, at least 46, at least 47, at least 48, at least 49, at least 50, at least 55, at least 60, at least 70, at least 75, at least 80, at least 85, at least 90, at least 95, at least 100, at least 110, at least 120, at least 130, at least 140, or at least 150 amino acids (which may or may not be consecutive amino acids). In some embodiments, a modification comprises a deletion, addition, or substitution of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59,

60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81,82,83,84, 85,

86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 105, 110, 115, 120, 125, 130, 140, or

150 amino acids (which may or may not be consecutive amino acids).

In some embodiments, a modified polymerase comprises one or more unnatural amino acid substitutions. As used herein, an“unnatural amino acid” refers to any amino acid, modified amino acid, or amino acid analogue other than the following twenty genetically encoded alpha- amino acids: alanine, arginine, asparagine, aspartic acid, cysteine, glutamine, glutamic acid, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, valine. In some embodiments, unnatural amino acids may include naturally occurring compounds other than the twenty alpha-amino acids above.

Unnatural amino acids and methods of incorporating unnatural amino acids into protein sequences are known in the art, for example, as described in U.S. Patent No. 7,045,337, the contents of which are incorporated herein by reference.

A. Amino Acid Modification Designations

A modification may be designated by a position within an amino acid sequence. For example, a modification may be designated“A484,” indicating that the alanine residue at position 484 in the amino acid sequence of the polymerase has been modified (thereby producing the modified polymerase). Modifications may also be designated by the position/identity of a corresponding amino acid of a reference polymerase.

For example, in some embodiments, a modified polymerase comprises a mutation at a position corresponding to A484 in F29 polymerase (SEQ ID NO: 1). An amino acid

corresponding to A484 in other polymerases can be determined by any method known in the art, including homology alignment. See e.g., FIG. 5B and FIG. 17.

As a non-limiting example of this analysis, a homology alignment was conducted with a number of the polymerases reported in TABLE 1, and it was determined that A484 in F29 polymerase corresponds to A481 in M2Y, A492 in Bacillus phage VMY22, K500 in

Enterococcus faecium, and K827 in Lucilia cuprina. Accordingly, homology alignments and similar methods known in the art may be used to identify amino acids in other polymerases corresponding to the positions of the modified residues described herein. Thus, it should be appreciated that the modifications of the disclosure are not intended to be limited to the polymerases described herein (e.g., those listed in TABLE 1) and can be extended to any polymerizing enzyme using known techniques.

In some embodiments, the sequence of a polymerase that is modified does not comprise one or more amino acids (i.e., one or more“homologous amino acids”) that correspond to a position in a reference polymerase (e.g., a polymerase listed in TABLE 1). As such, in some embodiments, a polymerase is modified by addition (or insertion) of a homologous amino acid at the designated reference position, which is inferred based on the surrounding homologous residues of the polymerase that is modified. Mutated polymerase variants comprising

homologous amino acids were engineered in accordance with embodiments described herein and are listed in TABLE 3.

(i) Amino Acid Modifications in Reference to E. faecium polymerase.

In some embodiments, an amino acid modification is made to a polymerase (e.g., a polymerase listed in TABLE 1), wherein the amino acid modification is made in reference to E. faecium polymerase (SEQ ID NOs: 2-5). For example, in some embodiments, a modified polymerase comprises an amino acid modification (i.e., mutation) at one or more positions (e.g., at 1-117 positions or any whole number between, for example 2 or more, 5 or more, 10 or more, 15 or more, 20 or more, for example all - and in any combination, thereof) corresponding to K4, T13, S22, V25, C26, D27, N33, 134, F36, S42, D54, N59, E60, E65, E85, M95, N106, T110, T114, K119, Q122, Y133, P136, E139, E142, N145, P147, 1148, E152, 1153, P160, D167, D171, N175, F188, D189, Q206, T211, S216, R217, D232, A236, V247, 1253, V261, L264, S267,

P273, P275, R308, V315, Q317, S319, L320, 1322, Q323, D337, E338, D341, T345, F352, F353, T364, D374, 1384, E385, N388, E391, A396, N397, G400, D414, D425, R429, E436, L437, V443, L445, A446, S447, V449, T450, W452, G453, Y455, F465, N467, T479, E482, A484, E485, A486, L490, D492, S493, K495, K500, S503, Q506, Q513, E519, D521, E523, V526, D533, R534, E537, G547, E545, L555, P556, R558, T559, V564, T568, M569, and T571 in E. faecium polymerase (SEQ ID NO: 2).

Such a modification may comprise a deletion (e.g., a deletion of an amino acid at a position corresponding to K4, T13, S22, V25, C26, D27, N33, 134, F36, S42, D54, N59, E60, E65, E85, M95, N106, T110, T114, K119, Q122, Y133, P136, E139, E142, N145, P147, 1148, E152, 1153, PI 60, D167, D171, N175, F188, D189, Q206, T211, S216, R217, D232, A236, V247, 1253, V261, L264, S267, P273, P275, R308, V315, Q317, S319, L320, 1322, Q323, D337, E338, D341, T345, F352, F353, T364, D374, 1384, E385, N388, E391, A396, N397, G400, D414, D425, R429, E436, L437, V443, L445, A446, S447, V449, T450, W452, G453, Y455, F465, N467, T479, E482, A484, E485, A486, L490, D492, S493, K495, K500, S503, Q506, Q513, E519, D521, E523, V526, D533, R534, E537, G547, E545, L555, P556, R558, T559, V564, T568, M569, or T571 (or any combination thereof) in E. faecium polymerase (SEQ ID NO: 2)).

Alternatively, or in addition, such a modification may comprise an addition (e.g., an addition of a homologous amino acid at a position corresponding to K4, T13, S22, V25, C26, D27, N33, 134, F36, S42, D54, N59, E60, E65, E85, M95, N106, T110, T114, K119, Q122, Y133, P136, E139, E142, N145, P147, 1148, E152, 1153, P160, D167, D171, N175, F188, D189, Q206, T211, S216, R217, D232, A236, V247, 1253, V261, L264, S267, P273, P275, R308,

V315, Q317, S319, L320, 1322, Q323, D337, E338, D341, T345, F352, F353, T364, D374, 1384, E385, N388, E391, A396, N397, G400, D414, D425, R429, E436, L437, V443, L445, A446, S447, V449, T450, W452, G453, Y455, F465, N467, T479, E482, A484, E485, A486, L490, D492, S493, K495, K500, S503, Q506, Q513, E519, D521, E523, V526, D533, R534, E537, G547, E545, L555, P556, R558, T559, V564, T568, M569, or T571 (or any combination thereof) in E. faecium polymerase (SEQ ID NO: 2)).

Alternatively, or in addition, such a modification may comprise a substitution. For example, a modification may comprise a substitution at one or more positions (e.g., at 1-117 positions or any whole number between, for example 2 or more, 5 or more, 10 or more, 15 or more, 20 or more, for example all - and in any combination, thereof) corresponding to K4, T13, S22, V25, C26, D27, N33, 134, F36, S42, D54, N59, E60, E65, E85, M95, N106, T110, T114, K119, Q122, Y133, P136, E139, E142, N145, P147, 1148, E152, 1153, P160, D167, D171, N175, F188, D189, Q206, T211, S216, R217, D232, A236, V247, 1253, V261, L264, S267, P273,

P275, R308, V315, Q317, S319, L320, 1322, Q323, D337, E338, D341, T345, F352, F353, T364, D374, 1384, E385, N388, E391, A396, N397, G400, D414, D425, R429, E436, L437, V443, L445, A446, S447, V449, T450, W452, G453, Y455, F465, N467, T479, E482, A484, E485, A486, L490, D492, S493, K495, K500, S503, Q506, Q513, E519, D521, E523, V526, D533, R534, E537, G547, E545, L555, P556, R558, T559, V564, T568, M569, and T571 in E. faecium polymerase (SEQ ID NO: 2). In some embodiments, a substitution is selected from the group consisting of K4R, T13N, S22A, V25L, C26W, D27E, N33T, I34V, F36V, S42T, D54Y, N59D, E60L, E60V, E65S, E85P, M95T, M95K, N106G, T110I, T114S, K119Q, Q122V, Y133L, P136T, E139K, E139Q, E139R, E139H, E142K, E142Q, E142R, E142H, N145K, N145H, N145R, P147Q, P147T, I148K, I148H, I148R, E152D, I153V, P160A, D167P, D167K, D167H, D167R, D171K, D171H, D171R, N175T, N175Y, F188C, D189K, D189H, D189R, Q206R, Q206K, Q206H, T211A, S216G, S216R, R217G, D232K, A236G, V247D, I253H, I253A, V261A, V261I, V261L, L264H, L264A, L264M, S267A, P273S, P273R, P275S, E283K,

V315L, S319R, R308G, G308R, Q317R, S319R, L320M, L320T, I322K, Q323G, Q323V, Q323R, D337G, E338K, D341T, T345I, F352I, F353C, T364I, D374G, D374Q, D374H, I384T, I384F, I384S, E385Y, E385K, E385R, E385N, E385Q, E385L, E385A, N388T, E391Y, E391W, E391F, E391H, E391M, E391K, E391R, A396Q, N397L, G400L, D414V, D425N, R429G, E436R, E436G, L437Y, L437E, V443T, L445M, A446G, S447V, V449I, T450A, W452Y, G453A, Y455W, F465Y, N467R, N467K, N467H, N467S, N467T, T479V, E482K, E482H, E482R, A484E, E485D, A486E, L490M, D492H, D492K, D492R, D492A, H492S, S493P, K495R, K500E, S503A, S503T, Q506K, Q513D, D521K, D521R, D521H, E523R, E523V, E523Y, E523F, E523H, E523W, V526L, D533A, D533Q, D533T, D533R, D533S, R534K, E537K, E537H, E537R, E545K, E545H, E545R, G547S, L555K, L555R, P556A, R558H, T559V, V564L, T568D, T568S, M569K, M569T, M569V, and T571S (corresponding to positions in E. faecium polymerase (SEQ ID NO: 2)).

Exemplary modification combinations are listed in TABLE 7.

(ii) Amino Acid Modifications in Reference to F29 polymerase.

In some embodiments, an amino acid modification is made to a polymerase (e.g., a polymerase listed in TABLE 1), wherein the amino acid modification is made in reference to F29 polymerase (SEQ ID NO: 1). For example, in some embodiments, a modified polymerase comprises an amino acid modification (i.e., mutation) at one or more positions (e.g., 2 or more, 5 or more, 10 or more, 15 or more, 20 or more, for example 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13,

14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39,

40, 41, 42, 43, or 44 positions - in any combination, thereof) corresponding to M8, V51, N62, 171, L107, K131, K135, L142, G135, L142, Y148, G197, Y224, Y226, E239, V250, N251, L253, Y281, 1288, T301, R306, R308, D325, D341, K354, T368, E375, K379, Q380, A437, A444, P447, E466, D476, K478, A484, E508, D510, K512, E515, K539, D570, or T571 in F29 polymerase.

Such a modification may comprise a deletion (e.g., a deletion of an amino acid at a position corresponding to M8, V51, N62, 171, L107, K131, K135, L142, G135, L142, Y148, G197, Y224, Y226, E239, V250, N251, L253, Y281, 1288, T301, R306, R308, D325, D341, K354, T368, E375, K379, Q380, A437, A444, P447, E466, D476, K478, A484, E508, D510, K512, E515, K539, D570, or T571 (or any combination thereof) in F29 polymerase).

Alternatively, or in addition, such a modification may comprise an addition (e.g., an addition of a homologous amino acid at a position corresponding to M8, V51, N62, 171, L107, K131, K135, L142, G135, L142, Y148, G197, Y224, Y226, E239, V250, N251, L253, Y281, 1288, T301, R306, R308, D325, D341, K354, T368, E375, K379, Q380, A437, A444, P447, E466, D476, K478, A484, E508, D510, K512, E515, K539, D570, or T571 (or any combination thereof) in F29 polymerase).

Alternatively, or in addition, such a modification may comprise a substitution. For example, a modification may comprise a substitution at one or more positions (e.g., at 1-44 positions or any whole number between, for example 2 or more, 5 or more, 10 or more, 15 or more, 20 or more, for example all - and in any combination, thereof) corresponding to M8, V51, N62, 171, L107, K131, K135, L142, G135, L142, Y148, G197, Y224, Y226, E239, V250, N251, L253, Y281, 1288, T301, R306, R308, D325, D341, K354, T368, E375, K379, Q380, A437, A444, P447, E466, D476, K478, A484, E508, D510, K512, E515, K539, D570, and T571 in F29 polymerase. In some embodiments, a substitution is selected from the group consisting of M8R, V51A, N62D, 17 IV, L107I, K131E, K135Q, L142K, Y148I, G197D, Y224K, Y226F, E239G, V250A, V250I, N251R, L253A, L253H, Y281H, I288L, T301C, R306Q, R308L, D325E,

D341E, K354R, T368F, E375K, E375Y, K379R, Q380R, A437G, A444T, E466K, D476H, P477D, K478D, A484C, A484Q, A484N, A484E, A484D, A484K, A484R, A484H, A484Y, and A484X (where X represents an unnatural amino acid, as described herein), E508R, D510K, D510R, K512Y, E515Q, K539E, D570S, and T571V (corresponding to positions in F29 polymerase).

In some embodiments, a modified polymerase comprises one or more (e.g., 2 or more, 5 or more, 10 or more, 15 or more, 20 or more, for example all) amino acid mutations at positions corresponding to K131, K135, L142, Y148, Y224, E239, V250, L253, R306, R308, E375, A437, E466, D476, A484, E508, D510, K512, E515, K539, D570, and T571 in F29 polymerase.

B. Majority Polymerase Sequences

In some embodiments, modified polymerizing enzymes provided by the disclosure comprise a polymerase sequence according to a wild-type polymerase sequence (e.g., as set forth in TABLE 1) with one or more modifications (e.g., as exemplified in TABLES 2-6, or combinations of two or more thereof). In some embodiments, a wild-type polymerase amino acid sequence (e.g., as set forth in TABLE 1) provides a majority polymerase sequence in which one or more modifications may be made to generate a modified polymerase. As used herein, a “majority polymerase sequence” or“majority sequence” of a modified polymerase refers to a wild-type polymerase amino acid sequence that predominates within the modified polymerase amino acid sequence (e.g., where at least 50% of the amino acids in the modified polymerase sequence corresponds to amino acids in the majority sequence). In some embodiments, a modified polymerase sequence comprises a majority sequence further comprising one or more amino acid mutations. In some embodiments, one or more amino acid mutations comprise amino acids at positions corresponding to positions in homologous proteins. In some embodiments, a polymerase amino acid sequence set forth in any one of Tables 2-6 provides a majority polymerase sequence in which one or more modifications may be made to generate a modified polymerase.

In some embodiments, a modified polymerase has at least 25% amino acid sequence identity to one or more of the polymerases listed in TABLE 1 (e.g., to SEQ ID NO: 1, SEQ ID NOs: 2-5, SEQ ID Nos: 6-22, or SEQ ID Nos: 23-33 listed in TABLE 1). In some

embodiments, a modified polymerase has 25-50%, 50-60%, 60-70%, 70-80%, 80-90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or higher amino acid sequence identity to one or more of the polymerases listed in TABLE 1 (e.g., to SEQ ID NO: 1, SEQ ID NOs: 2-5, SEQ ID Nos: 6-22, or SEQ ID Nos: 23-33 listed in TABLE 1). In some embodiments, a modified polymerase has 25-50%, 50-60%, 60-70%, 70-80%, 80-90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or higher amino acid sequence identity to any one of SEQ ID Nos: 2-5. In some embodiments, a modified polymerase has 25-50%, 50-60%, 60-70%, 70-80%, 80-90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or higher amino acid sequence identity to SEQ ID NO: 2. In some embodiments, a modified polymerase has 25-50%, 50-60%, 60-70%, 70-80%, 80-90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or higher amino acid sequence identity to any one of SEQ ID Nos: 23-33. In some embodiments, such a modified polymerase includes one or more of the amino acid mutations and/or domain substitutions described in the context of different modified polymerase configurations and/or examples provided in this application. In some embodiments, the only modifications in a modified polymerase are one or more of the modifications (e.g., amino acid substitutions) provided in this disclosure and the sequence of the polymerase is otherwise identical to a wild-type polymerase (e.g., a sequence of TABLE 1) or to a sequence described in any of TABLES 2-7.

Sequence identity may be in reference to the entire amino acid sequence of the modified polymerase. However, in some embodiments, sequence identity is in reference to one or more segments, subdomains, or domains of the modified polymerase. For example, in some embodiments, one or more segment, subdomain, or domain of a modified polymerase is described as having at least 50% amino acid sequence identity to a segment, subdomain, or domain of a reference polymerase listed in TABLE 1 (e.g., to SEQ ID NO: 1, SEQ ID NOs: 2-5, SEQ ID Nos: 6-22, or SEQ ID Nos: 23-33 listed in TABLE 1). Such segments, subdomains or domains may have, for example, 50-60%, 60-70%, 70-80%, 80-90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to a corresponding segment, subdomain, or domain of a reference polymerase listed in TABLE 1 (e.g., to SEQ ID NO: 1, SEQ ID NOs: 2- 5, SEQ ID Nos: 6-22, or SEQ ID Nos: 23-33 listed in TABLE 1). In some embodiments, such segments, subdomains or domains may have, for example, 50-60%, 60-70%, 70-80%, 80-90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to a

corresponding segment, subdomain, or domain of any one of SEQ ID Nos: 2-5. In some embodiments, such segments, subdomains or domain may have, for example, 50-60%, 60-70%, 70-80%, 80-90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to a corresponding segment, subdomain, or domain of SEQ ID NO: 2. In some embodiments, such segments, subdomains or domains may have, for example, 50-60%, 60-70%, 70-80%, 80- 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity to a corresponding segment, subdomain, or domain of any one of SEQ ID NOs: 23-33.

For the purposes of comparing two or more amino acid sequences, the percentage of “sequence identity” between a first amino acid sequence and a second amino acid sequence (also referred to herein as“amino acid identity”) may be calculated by dividing [the number of amino acid residues in the first amino acid sequence that are identical to the amino acid residues at the corresponding positions in the second amino acid sequence] by [the total number of amino acid residues in the first amino acid sequence] and multiplying by [100%], in which each deletion, insertion, substitution or addition of an amino acid residue in the second amino acid sequence - compared to the first amino acid sequence - is considered as a difference at a single amino acid residue (position), i.e., as an“amino acid difference” as defined herein. Alternatively, the degree of sequence identity between two amino acid sequences may be calculated using a known computer algorithm (e.g., by the local homology algorithm of Smith and Waterman (1970) Adv. Appl. Math. 2:482c, by the homology alignment algorithm of Needleman and Wunsch, J. Mol. Biol. (1970) 48:443, by the search for similarity method of Pearson and Lipman. Proc. Natl. Acad. Sci. USA (1998) 85:2444, or by computerized implementations of algorithms available as Blast, Clustal Omega, or other sequence alignment algorithms) and, for example, using standard settings. Usually, for the purpose of determining the percentage of“sequence identity” between two amino acid sequences in accordance with the calculation method outlined hereinabove, the amino acid sequence with the greatest number of amino acid residues will be taken as the“first” amino acid sequence, and the other amino acid sequence will be taken as the“second” amino acid sequence. Additionally, or alternatively, two or more sequences may be assessed for the identity between the sequences. The terms“identical” or percent“identity” in the context of two or more nucleic acids or amino acid sequences, refer to two or more sequences or subsequences that are the same. Two sequences are“substantially identical” if two sequences have a specified percentage of amino acid residues or nucleotides that are the same (e.g., at least 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.6%, 99.7%, 99.8% or 99.9% identical) over a specified region or over the entire sequence, when compared and aligned for maximum correspondence over a comparison window, or designated region as measured using one of the following sequence comparison algorithms or by manual alignment and visual inspection. Optionally, the identity exists over a region that is at least about 25, 50, 75, or 100 amino acids in length, or more preferably over a region that is 100 to 150, 200 or more amino acids in length.

Additionally, or alternatively, two or more sequences may be assessed for the alignment between the sequences. The terms“alignment” or percent“alignment” in the context of two or more nucleic acids or amino acid sequences, refer to two or more sequences or subsequences that are the same. Two sequences are "substantially aligned" if two sequences have a specified percentage of amino acid residues or nucleotides that are the same (e.g., at least 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.6%, 99.7%, 99.8% or 99.9% identical) over a specified region or over the entire sequence, when compared and aligned for maximum correspondence over a comparison window, or designated region as measured using one of the following sequence comparison algorithms or by manual alignment and visual inspection. Optionally, the alignment exists over a region that is at least about 25, 50, 75, or 100 amino acids in length, or more preferably over a region that is 100 to 150, 200 or more amino acids in length.

(i) Modified E. faecium Polymerases

The present application is based in part on the recognition that a polymerase from E. faecium can be advantageously utilized as a reagent in in vitro polymerization reactions, such as single-molecule nucleic acid sequencing reactions. The inventors have recognized that the wild- type E. faecium polymerase displays robust strand displacement activity, high processivity with nucleotide substrates (e.g., greater than 70 kilobases), and an ability to utilize synthetic nucleotide analogs. FIG. 24 shows results from rolling-circle assays assessing the processivity of wild-type EF polymerase compared to known processive polymerase QTDE1.0. The inventors have further recognized that certain modifications (e.g., mutations, insertions, and/or

substitutions) to the wild-type E. faecium polymerase further enhance these and other functional attributes to provide an improved reagent for nucleic acid sequencing reactions. As such, in some embodiments, a modified polymerase is a modified E. faecium polymerase (i.e., comprises a E. faecium polymerase majority sequence, such as any one of SEQ ID NOs: 2-5). FIG. 13A shows sequence identity between four naturally occurring E. faecium polymerase variants. FIG. 13B shows sequences identity shared between the variants. Sequences are listed by their NCBI protein database accession numbers. In some embodiments, a modified polymerase comprises a E. faecium polymerase majority sequence of SEQ ID NO: 2.

In some embodiments, a modified E. faecium polymerase comprises an amino acid modification (i.e., mutation) at one or more positions (e.g., at 1-117 positions or any whole number between, for example 2 or more, 5 or more, 10 or more, 15 or more, 20 or more, for example all - and in any combination, thereof) corresponding to K4, T13, S22, V25, C26, D27, N33, 134, F36, S42, D54, N59, E60, E65, E85, M95, N106, T110, T114, K119, Q122, Y133, P136, E139, E142, N145, P147, 1148, E152, 1153, P160, D167, D171, N175, F188, D189, Q206, T211, S216, R217, D232, A236, V247, 1253, V261, F264, S267, P273, P275, R308, V315, Q317, S319, F320, 1322, Q323, D337, E338, D341, T345, F352, F353, T364, D374, 1384, E385, N388, E391, A396, N397, G400, D414, D425, R429, E436, F437, V443, F445, A446, S447, V449, T450, W452, G453, Y455, F465, N467, T479, E482, A484, E485, A486, F490, D492, S493, K495, K500, S503, Q506, Q513, E519, D521, E523, V526, D533, R534, E537, G547, E545, F555, P556, R558, T559, V564, T568, M569, and T571 in the reference E. faecium polymerase. A modified E. faecium polymerase may comprise one or more amino acid modifications relative to SEQ ID Nos: 2-5 or a sequence described in TABLE 2 or TABLE 7.

Such a modification may comprise a deletion (e.g., a deletion of an amino acid at a position corresponding to K4, T13, S22, V25, C26, D27, N33, 134, F36, S42, D54, N59, E60, E65, E85, M95, N106, T110, T114, K119, Q122, Y133, P136, E139, E142, N145, P147, 1148, E152, 1153, PI 60, D167, D171, N175, F188, D189, Q206, T211, S216, R217, D232, A236, V247, 1253, V261, L264, S267, P273, P275, R308, V315, Q317, S319, L320, 1322, Q323, D337, E338, D341, T345, F352, F353, T364, D374, 1384, E385, N388, E391, A396, N397, G400, D414, D425, R429, E436, L437, V443, L445, A446, S447, V449, T450, W452, G453, Y455, F465, N467, T479, E482, A484, E485, A486, L490, D492, S493, K495, K500, S503, Q506, Q513, E519, D521, E523, V526, D533, R534, E537, G547, E545, L555, P556, R558, T559, V564, T568, M569, or T571 (or any combination thereof) in the reference E. faecium

polymerase.

Alternatively, or in addition, such a modification may comprise an addition (e.g., an addition of a homologous amino acid at a position corresponding to K4, T13, S22, V25, C26, D27, N33, 134, F36, S42, D54, N59, E60, E65, E85, M95, N106, T110, T114, K119, Q122, Y133, P136, E139, E142, N145, P147, 1148, E152, 1153, P160, D167, D171, N175, F188, D189, Q206, T211, S216, R217, D232, A236, V247, 1253, V261, L264, S267, P273, P275, R308,

V315, Q317, S319, L320, 1322, Q323, D337, E338, D341, T345, F352, F353, T364, D374, 1384, E385, N388, E391, A396, N397, G400, D414, D425, R429, E436, L437, V443, L445, A446, S447, V449, T450, W452, G453, Y455, F465, N467, T479, E482, A484, E485, A486, L490, D492, S493, K495, K500, S503, Q506, Q513, E519, D521, E523, V526, D533, R534, E537, G547, E545, L555, P556, R558, T559, V564, T568, M569, or T571 (or any combination thereof) in the reference E. faecium polymerase).

Alternatively, or in addition, such a modification may comprise a substitution. For example, a modification may comprise a substitution at one or more positions (e.g., at 1-117 positions or any whole number between, for example 2 or more, 5 or more, 10 or more, 15 or more, 20 or more, for example all - and in any combination, thereof) corresponding to K4, T13, S22, V25, C26, D27, N33, 134, F36, S42, D54, N59, E60, E65, E85, M95, N106, T110, T114, K119, Q122, Y133, P136, E139, E142, N145, P147, 1148, E152, 1153, P160, D167, D171, N175, F188, D189, Q206, T211, S216, R217, D232, A236, V247, 1253, V261, F264, S267, P273,

P275, R308, V315, Q317, S319, F320, 1322, Q323, D337, E338, D341, T345, F352, F353, T364, D374, 1384, E385, N388, E391, A396, N397, G400, D414, D425, R429, E436, F437, V443, L445, A446, S447, V449, T450, W452, G453, Y455, F465, N467, T479, E482, A484, E485, A486, F490, D492, S493, K495, K500, S503, Q506, Q513, E519, D521, E523, V526, D533, R534, E537, G547, E545, F555, P556, R558, T559, V564, T568, M569, and T571 in E. faecium polymerase. In some embodiments, a substitution is selected from the group consisting of K4R, T13N, S22A, V25F, C26W, D27E, N33T, I34V, F36V, S42T, D54Y, N59D, E60F, E60V,

E65S, E85P, M95T, M95K, N106G, T110I, T114S, K119Q, Q122V, Y133F, P136T, E139K, E139Q, E139R, E139H, E142K, E142Q, E142R, E142H, N145K, N145H, N145R, P147Q, P147T, I148K, I148H, I148R, E152D, I153V, P160A, D167P, D167K, D167H, D167R, D171K, D171H, D171R, N175T, N175Y, F188C, D189K, D189H, D189R, Q206R, Q206K, Q206H, T211A, S216G, S216R, R217G, D232K, A236G, V247D, I253H, I253A, V261A, V261I,

V261F, F264H, F264A, F264M, S267A, P273S, P273R, P275S, E283K, V315F, S319R,

R308G, G308R, Q317R, S319R, F320M, F320T, I322K, Q323G, Q323V, Q323R, D337G, E338K, D341T, T345I, F352I, F353C, T364I, D374G, D374Q, D374H, I384T, I384F, I384S, E385Y, E385K, E385R, E385N, E385Q, E385F, E385A, N388T, E391Y, E391W, E391F, E391H, E391M, E391K, E391R, A396Q, N397F, G400F, D414V, D425N, R429G, E436R, E436G, F437Y, F437E, V443T, F445M, A446G, S447V, V449I, T450A, W452Y, G453A, Y455W, F465Y, N467R, N467K, N467H, N467S, N467T, T479V, E482K, E482H, E482R, A484E, E485D, A486E, L490M, D492H, D492K, D492R, D492A, H492S, S493P, K495R, K500E, S503A, S503T, Q506K, Q513D, D521K, D521R, D521H, E523R, E523V, E523Y, E523F, E523H, E523W, V526L, D533A, D533Q, D533T, D533R, D533S, R534K, E537K, E537H, E537R, E545K, E545H, E545R, G547S, L555K, L555R, P556A, R558H, T559V,

V564L, T568D, T568S, M569K, M569T, M569V, and T571S (corresponding to positions in the reference E. faecium polymerase).

Exemplary modification combinations are listed in TABLE 7.

In some embodiments, a modified E. faecium polymerase does not comprise an amino acid modification (i.e., mutation) at one or more positions (e.g., 2 or more, 5 or more, 10 or more, 15 or more, 20 or more, for example 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, or 44 positions - in any combination, thereof) corresponding to M8, V51, N62, 171, L107, K131, K135, L142, G135, L142, Y148, G197, Y224, Y226, E239, V250, N251, L253, Y281, 1288, T301, R306, R308, D325, D341, K354, T368, E375, K379, Q380, A437, A444, P447, E466, D476, K478, A484, E508, D510, K512, E515, K539, D570, or T571 in F29 polymerase (SEQ ID NO: 1).

In some embodiments, a modified E. faecium polymerase comprises at least one modification that alters a characteristic of the polymerase relative to the reference E. faecium polymerase. For example, a modification may result in: increased (or, alternatively decreased) processivity; increased (or, alternatively decreased) nuclease activity; increased (or, alternatively decrease) accuracy; increased (or, alternatively decrease) nucleotide substrate utilization (of one or more substrates); increased (or alternatively decreased) affinity toward one or more substrates; increased (or alternatively decreased) replication capacity; increased (or alternatively decreased) average read length; increased (or alternatively decreased) electropositive charge at the surface; or increased (or, alternatively decreased) stability.

In some embodiments, a modified E. faecium polymerase comprises one or more modifications that improves processivity. For example, in some embodiments, a modified polymerase comprises a mutation at one or more positions corresponding to T568 and M569 in E. faecium polymerase. In some embodiments, a modified polymerase of the disclosure is a modified E. faecium polymerase comprising a mutation at one or both of T568 and M569. In some embodiments, the modified polymerase comprises one or more of: a mutation at T568 selected from T568D and T568S; and a mutation at M569 selected from M569T and M569V. In some embodiments, the modified E. faecium polymerase comprises mutations at each of T568 and K500. In some embodiments, a modified E. faecium polymerase comprises a modification that eliminates or reduces exonuclease activity. For example, in some embodiments, the modified E. faecium polymerase comprises a mutation at N59 that eliminates or reduces exonuclease activity. In some embodiments, the modified E. faecium polymerase comprises N59D. In some embodiments, a modified E. faecium polymerase does not comprise a mutation at N59 (e.g., the modified E. faecium polymerase comprises N59). It should be appreciated that a mutation at N59 in a modified E. faecium polymerase can be introduced or reverted back to wild-type depending on a desired functionality. Accordingly, in some embodiments, a modified E. faecium polymerase comprises a sequence selected from TABLE 2, further modified to introduce a mutation at N59 (e.g., further modified to comprise N59D). In some embodiments, a modified E. faecium polymerase comprises a sequence selected from TABLE 2, further modified to revert a mutation at N59 back to wild-type (e.g., further modified to comprise D59N).

In some embodiments, a modified E. faecium polymerase comprises one or more modifications that improves nucleotide substrate utilization at the active site. In some embodiments, such a modification enhances the incorporation of a nucleotide or nucleotide analog (e.g., a nucleotide hexaphosphate) into a newly synthesized nucleic acid strand in a polymerization reaction. For example, in some embodiments, a modified polymerase comprises a mutation at one or more positions corresponding to V261, L264, S267, 1384, E391, W452, G453, Y455, D492, and K500 in E. faecium polymerase. In some embodiments, a modified polymerase of the disclosure is a modified E. faecium polymerase comprising a mutation at one or more of V261, L264, S267, 1384, E391, W452, G453, Y455, D492, and K500. In some embodiments, the modified E. faecium polymerase comprises one or more of: a mutation at V261 selected from V261A and V261I; a mutation at L264 selected from L264A, L264H, and L264M; S267A; a mutation at 1384 selected from I384F and I384S; a mutation at E391 selected from E391Y, E391W, E391F, E391H, E391M, E391K, and E391R; W452Y; G453A; Y455W;

D492H; and K500E. In some embodiments, a modified polymerase of the disclosure is a modified E. faecium polymerase comprising mutations at each of V261, L264, S267, 1384, E391, W452, G453, Y455, D492, and K500. In some embodiments, the modified E. faecium polymerase comprises V261A, L264H, and K500E.

In some embodiments, a modified E. faecium polymerase comprises a segment insertion that improves nucleotide substrate utilization at the active site. For example, based on a structural homology analysis, it was determined that wild-type E. faecium polymerase does not contain a structural motif proximal to the active site as found in the palm domain of F29 polymerase. This structural motif, spanning D503 to K525 in the F29 sequence, forms favorable interactions with nucleotide analogs (e.g., nucleotide hexaphosphates), which improves performance in sequencing reactions. FIGs. 14A-14B show comparisons of E. faecium polymerase and F29. In some embodiments, an active site modification comprises a segment insertion that replaces amino acids at positions 519 through 522 in E. faecium polymerase (E519 through G522) with a segment corresponding to positions D503 through K525 in F29

polymerase (e.g., a segment comprising a sequence spanning D503 through K525 in F29 polymerase, or a homologous segment in M2Y polymerase). In some embodiments, the segment insertion comprises one or more mutations at positions corresponding to E508, D510, K512, and E515Q in F29 polymerase. In some embodiments, the segment insertion comprises one or more mutations selected from E508R, D510R, K512Y, and E515Q. In some embodiments, the segment insertion replaces amino acids at positions 519 through 522 in E. faecium polymerase (EIKG, SEQ ID NO: 840) with a segment comprising an amino acid sequence of

DIYAKRVRGYLIECSPDEATTTK (SEQ ID NO: 841). In some embodiments, the segment insertion replaces amino acids at positions 519 through 522 in E. faecium polymerase (EIKG, SEQ ID NO: 840) with a segment comprising an amino acid sequence of

DIYMKRVRGYLVQGSPDDYTDIK (SEQ ID NO: 842).

In some embodiments, a modified E. faecium polymerase comprises one or more modifications that enhance polymerization accuracy. For example, in some embodiments, a modified polymerase comprises a mutation at one or more positions corresponding to E65, Y 133, V261, L264, S267, 1384, E391, G400, V443, L445, A446, S447, V449, T450, W452, G453, Y455, K500, S503, E523, L555, and P556 in E. faecium polymerase. In some embodiments, a modified polymerase of the disclosure is a modified E. faecium polymerase comprising a mutation at one or more of E65, Y133, V261, L264, S267, 1384, E391, G400, V443, L445,

A446, S447, V449, T450, W452, G453, Y455, K500, S503, E523, L555, and P556. In some embodiments, a modified E. faecium polymerase comprises one or more of: E65S; Y 133L; a mutation at V261 selected from V261A and V261I; a mutations at L264 selected from L264A and L264H; S267A; a mutation at 1384 selected from I384F, I384S; a mutation a E391 selected from E391Y, E391W, E391F, and E391K; G400L; V443T; L445M; A446G; S447V; V449I; T450A; W452Y; G453A, Y455W; K500E; S503A; a mutation a E523 selected from E523K, E523Y, E523F, E523H, and E523W; L555K; and P556A.

In some embodiments, a modified E. faecium polymerase comprises one or more modifications that enhance DNA binding. For example, in some embodiments, a modified polymerase comprises a mutation at one or more positions corresponding to Q317, S319, 1322, Q323, R429, L555, and T559 in E. faecium polymerase. In some embodiments, a modified polymerase of the disclosure is a modified E. faecium polymerase comprising a mutation at one or more of Q317, S319, 1322, Q323, R429, L555, and T559. In some embodiments, the modified polymerase comprises one or more of: Q317R; S319R; I322K; Q323G; R429G; L555K; and T559V.

In some embodiments, a modified E. faecium polymerase comprises one or more modifications that enhance analog binding. For example, in some embodiments, a modified polymerase comprises a mutation at one or more positions corresponding to E391, S503 and E523 in E. faecium polymerase. In some embodiments, a modified polymerase of the disclosure is a modified E. faecium polymerase comprising a mutation at one or more of E391, S503 and E523. In some embodiments, the modified polymerase comprises one or more of: at mutation at E391 selected from E391Y, E391W, E391F, and E391K; S503A; and a mutation at E523 selected from E523K, E523Y, E523F, E523H, and E523W.

In some embodiments, a modified E. faecium polymerase comprises one or more modifications that enhance strand displacement. For example, in some embodiments, a modified polymerase comprises a mutation at one or more positions corresponding to Q206, E436 and L437 in E. faecium polymerase. In some embodiments, a modified polymerase of the disclosure is a modified E. faecium polymerase comprising a mutation at one or more of Q206, E436 and L437. In some embodiments, the modified polymerase comprises one or more of: a mutation at Q206 selected from Q206R, Q206K and Q206H; E436R; and a mutation at L437 selected from L437Y and L437E.

In some embodiments, a modified E. faecium polymerase comprises one or more modifications that enhance average read length. For example, in some embodiments, a modified polymerase comprises a mutation at one or more positions corresponding to E436, L437, R534, T568, and M569 in E. faecium polymerase. In some embodiments, a modified E. faecium polymerase comprises a mutation at one or more of E436, L437, R534, T568, and M569. In some embodiments, the modified polymerase comprises one or more of: E436R; a mutation at L437 selected from L437Y and L437E; R534K; a mutation at T568 selected from T568D and T568S; and a mutation at M569 selected from M569T and M569V.

In some embodiments, a modified E. faecium polymerase comprises one or more modifications that enhance replication capacity (e.g., at 45°C). For example, in some

embodiments, a modified polymerase comprises a mutation at one or more positions

corresponding to T13, V25, C26, D27, N33, 134, F36, S42, D54, E60, M95, T110, T114, K119, P136, P147, E152, 1153, P160, N175, F188, S216, R217, D232, A236, V247, P273, P275, E283, V315, S319, L320, Q323, E338, T345, F352, F353, T364, D414, D425, E436, F465, E485, A486, L490, S503, E523, V526, G547, L555, R558,V564, M569, and T571 in E. faecium polymerase. In some embodiments, a modified polymerase of the disclosure is a modified E. faecium polymerase comprising a mutation at one or more of T13, V25, C26, D27, N33, 134,

F36, S42, D54, E60, M95, T110, T114, K119, P136, P147, E152, 1153, P160, N175, F188, S216, R217, D232, A236, V247, P273, P275, E283, V315, S319, L320, Q323, E338, T345, F352,

F353, T364, D414, D425, E436, F465, E485, A486, L490, S503, E523, V526, G547, L555, R558,V564, M569, and T571. In some embodiments, the modified polymerase comprises one or more of: T13N; V25L; C26W; D27E; N33T; I34V; F36V; S42T; D54Y; E60V; a mutation at position M95 selected from M95T and M95K; T110I; T114S; K119Q; P136T; a mutation a position P147 selected from P147Q and P147T; E152D; I153V; P160A; N175Y; F188C; a mutation at position S216 selected from S216G and S216R; R217G; D232H; A236G; V247D; P273R; P275S; E283K; V315L; S319R; a mutation at position L320 selected from L320M and L320T; Q323R; E338K; T345I; F352I; F353C; T364I; D414V; D425N; E436G; F465Y; E485D; A486E; L490M; S503T; E523V; V526L; G547S; L555R; R558H; V564L; M569K; and T571S.

In some embodiments, a modified E. faecium polymerase comprises one or more modifications that increase electropositive charge at the protein surface. Similarly, in some embodiments, a modified E. faecium polymerase comprises an increased isoelectric point. In some embodiments, a modified E. faecium polymerase has an isoelectric point that is 0.1, 0.2,

0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.0-1.5, 1.5-2.0, 2.0-2.5, 2.5-3.0, 3.0-3.5, 3.5-4.0, 4.0-4.5, 5.0- 5.5, 5.5-6.0, 6.0-6.5, 6.5-7.0, 7.0-7.5, 7.5-8.0, 8.0-8.5, 8.5-9.0, 9.0-9.5, or 9.5-10.0 isoelectric point (pi) units higher than the isolectric point of wild-type E. faecium polymerase (e.g., SEQ ID NO: 2). Methods of measuring surface charge and isoelectric points are known to those having ordinary skill in the art. The isoelectric point (pi) is a standard concept in protein biochemistry with which the skilled person would be familiar. The pi is the pH value at which a protein displays a net charge of zero. An increase in pi means that a higher pH value is required for the protein to display a net charge of zero. Thus, an increase in pi represents an increase in the net positive charge of a protein at a given pH. Methods of determining the pi of a protein are known in the art. For example, the pi of a protein can be calculated from the average pKa values of each amino acid present in the protein ("calculated pi"). Such calculations can be performed using computer programs known in the art (e.g., Protein Calculator from the Scripps Research Institute and Compute pi/ W Tool from ExPASy). Comparisons of pi values between different molecules should be made using the same calculation technique/program. Where appropriate, the calculated pi of a protein can be confirmed experimentally using the technique of isoelectric focusing ("observed pi"). This technique uses electrophoresis to separate proteins according to their pi. Isoelectric focusing is typically performed using a gel that has an immobilised pH gradient. When an electric field is applied, the protein migrates through the pH gradient until it reaches the pH at which it has zero net charge, this point being the pi of the protein. Results provided by isoelectric focusing may be relatively low-resolution in nature, and thus in some embodiments, the results provided by calculated pi (as described above) are more appropriate to use.

In some embodiments, such surface charge modifications enhance the rate of

incorporation of nucleotide analogs that comprise an electronegative component (e.g., a nucleic acid linker) by providing a protein surface that is more attractive toward the nucleotide analog. In some embodiments, a modified polymerase comprises a mutation at one or more positions corresponding to E139, E142, N145, 1148, D167, D171, D189, D374, E385, E391, N467, E482, D492, K495, D521, E523, D533, E537, and E545 in E. faecium polymerase. In some embodiments, a modified polymerase of the disclosure is a modified E. faecium polymerase comprising a mutation at one or more of E139, E142, N145, 1148, D167, D171, D189, D374, E385, E391, N467, E482, D492, K495, D521, E523, D533, E537, and E545. In some embodiments, the modified polymerase comprises one or more of: a mutation at E139 selected from E139K, E139Q, E139R, and E139H; a mutation at E142 selected from E142K, E142H, E142R, and E142Q; a mutation at N145 selected from N145K, N145H, and N145R; a mutation at 1148 selected from I148K, I148H, and I148R; a mutation at D167 selected from D167P, D167K, D167H, and D167R; a mutation at D171 selected from D171K, D171H, and D171R; a mutation at D 189 selected from D189K, D189H, and D189R; a mutation at D374 selected from D374G, D374Q, and D374H; a mutation at E385 selected from E385Y, E385K, E385R, E385N, E385Q, E385L, and E385A; a mutation at E391 selected from E391Y, E391W, E391K, and E391F; a mutation a N467 selected from N467R, N467K, N467H, N467S, and N467T; a mutation at E482 selected from E482K, E482H, and E482R; a mutation at D492 selected from D492H, D492K, and D492R; K495R; a mutation at D521 selected from D521K, D521H, and D521R; a mutation at E523 selected from E523K, E523Y, E523H, E523R, E523F, and E523W; a mutation at D533 selected from D533A, D533Q, D533T, D533R, and D533S; a mutation at E537 selected from E537K, E537H, and E537R; and a mutation at E545 selected from E545K, E545H, and E545R.

In some embodiments, a modified E. faecium polymerase comprises one or more modifications that enhance protein stability (e.g., enhance thermostability, protein yield, and/or active polymerase population). For example, in some embodiments, a modified polymerase comprises a mutation at one or more positions corresponding to K4, S22, D27, 134, D54, E60, E85, M95, N106, T110, Q122, Y133, P136, P147, D167, T211, D232, P275, R308, S319, L320, E323, D337, E338, D341, T345, F352, T364, D414, F465, T479, E485, L490, S493, Q513, and R558 in E. faecium polymerase. In some embodiments, a modified polymerase of the disclosure is a modified E. faecium polymerase comprising a mutation at one or more of K4, S22, D27, 134, D54, E60, E85, M95, N106, T110, Q122, Y133, P136, P147, D167, T211, D232, P275, R308,

S319, L320, Q323, D337, E338, D341, T345, F352, T364, D414, F465, T479, E485, L490,

S493, Q513, and R558. In some embodiments, the modified polymerase comprises one or more of: K4R; S22A; D27E; I34V; D54Y; a mutation at E60 selected from E60V and E60L; E85P; M95K; T110I; N106G; Q122V; Y133L; P136T; a mutation at P147 selected from P147Q and P147T; D167P; T211A; D232K; P275S; R308G; S319R; L320M; Q323V; D337G; E338K; D341T; T345I; F352I; T364I; D414V; F465Y; T479V; E485D; L490M; S493P; Q513D; and R558H.

In some embodiments, a modified E. faecium polymerase comprises one or more modifications that enhance performance in a polymerization reaction (e.g., by improved accuracy, increased read length, and/or increased speed). In some embodiments, a modified polymerase comprises enhancing mutations at one or more positions corresponding to E142, V261, L264, S319, E391, L437, E482, D492, K500, E519, D521, E523, T568, and M569 in E. faecium polymerase. In some embodiments, a modified E. faecium polymerase comprises mutations at one or more of E142, V261, L264, S319, E391, L437, E482, D492, K500, E519, D521, E523, T568, and M569. In some embodiments, the modified polymerase comprises one or more of: a mutation at E142 selected from E142K and E142Q; a mutation at V261 selected from V261A and V261I; a mutation at L264 selected from L264A, L264H, and L264M; a mutation at E391 selected from E391Y, E391W, E391F, E391H, E391M, E391K, and E391R; a mutation at D521 selected from D521R and D521K; a mutation at E523 selected from E523Y and E523K; and a mutation selected from S319L, L437Y, E482K, D492H, K500E, E519R, T568S, and M569V.

It should be appreciated that, for the purposes of the disclosure, the E. faecium

polymerase modifications described herein may be classified according to different functional enhancements or different structural domains. Advantageously, a modified E. faecium polymerase of the disclosure comprises a plurality of modifications selected from the different functional and/or structural classifications described herein. This is exemplified by the modified E. faecium polymerase variants that were engineered in accordance with embodiments described herein, listed in TABLE 2. In some embodiments, a modified E. faecium polymerase comprises an amino acid sequence that is at least 25-50%, 50-60%, 60-70%, 70-80%, 80-90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to any one of SEQ ID Nos: 34-305, provided in TABLE 2. In some embodiments, a modified E. faecium polymerase comprises the amino acid sequence of any one of SEQ ID Nos: 34-305. In some embodiments, a modified E. faecium polymerase consists of an amino acid sequence that is at least 25-50%, 50-60%, 60-70%, 70-80%, 80-90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to any one of SEQ ID Nos: 34-305, provided in TABLE 2. In some embodiments, a modified E.

faecium polymerase consists of an amino acid sequence of any one of SEQ ID Nos: 34-305. In some embodiments, a modified E. faecium polymerase comprises an amino acid sequence that is at least 25-50%, 50-60%, 60-70%, 70-80%, 80-90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identical to SEQ ID NO: 88, SEQ ID NO: 157, or SEQ ID NO: 180. In some embodiments, a modified E. faecium polymerase comprises the amino acid sequence of SEQ ID NO: 88, SEQ ID NO: 157, or SEQ ID NO: 180. In some embodiments, a modified E. faecium polymerase consists of the amino acid sequence of SEQ ID NO: 88, SEQ ID NO: 157, or SEQ ID NO: 180.

In some embodiments, the only modifications in a modified polymerase are one or more of the modifications (e.g., amino acid substitutions in E. faecium polymerase) provided in this disclosure and the sequence of the polymerase is otherwise identical to a wild-type polymerase (e.g., SEQ ID Nos: 2-5) or to a sequence described in TABLE 2 or TABLE 7.

(ii) Modified F29 Polymerases

In some embodiments, a modified polymerase is a modified F29 polymerase (i.e., comprises a F29 polymerase majority sequence, such as SEQ ID NO: 1).

In some embodiments, a modified F29 polymerase comprises an amino acid modification (i.e., mutation) at one or more positions (e.g., 2 or more, 5 or more, 10 or more, 15 or more, 20 or more, for example 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, or 44 positions - in any combination, thereof) corresponding to M8, V51, N62, 171, L107, K131, K135, L142, G135, L142, Y148, G197, Y224, Y226, E239, V250, N251, L253, Y281, 1288, T301, R306, R308, D325, D341, K354, T368, E375, K379, Q380, A437, A444, P447, E466, D476, K478, A484, E508, D510, K512, E515, K539, D570, or T571 in the reference F29 polymerase.

Such a modification may comprise a deletion (e.g., a deletion of an amino acid at a position corresponding to M8, V51, N62, 171, L107, K131, K135, L142, G135, L142, Y148, G197, Y224, Y226, E239, V250, N251, L253, Y281, 1288, T301, R306, R308, D325, D341, K354, T368, E375, K379, Q380, A437, A444, P447, E466, D476, K478, A484, E508, D510, K512, E515, K539, D570, or T571 (or any combination thereof) in the reference F29 polymerase).

Alternatively, or in addition, such a modification may comprise an addition (e.g., an addition of a homologous amino acid at a position corresponding to M8, V51, N62, 171, L107, K131, K135, L142, G135, L142, Y148, G197, Y224, Y226, E239, V250, N251, L253, Y281, 1288, T301, R306, R308, D325, D341, K354, T368, E375, K379, Q380, A437, A444, P447, E466, D476, K478, A484, E508, D510, K512, E515, K539, D570, or T571 (or any combination thereof) in the reference F29 polymerase).

Alternatively, or in addition, such a modification may comprise a substitution. For example, a modification may comprise a substitution at one or more positions (e.g., at 1-44 positions or any whole number between, for example 2 or more, 5 or more, 10 or more, 15 or more, 20 or more, for example all - and in any combination, thereof) corresponding to M8, V51, N62, 171, L107, K131, K135, L142, G135, L142, Y148, G197, Y224, Y226, E239, V250, N251, L253, Y281, 1288, T301, R306, R308, D325, D341, K354, T368, E375, K379, Q380, A437, A444, P447, E466, D476, K478, A484, E508, D510, K512, E515, K539, D570, and T571 in F29 polymerase. In some embodiments, a substitution is selected from the group consisting of M8R, V51A, N62D, 17 IV, L107I, K131E, K135Q, L142K, Y148I, G197D, Y224K, Y226F, E239G, V250A, V250I, N251R, L253A, L253H, Y281H, I288L, T301C, R306Q, R308L, D325E,

D341E, K354R, T368F, E375K, E375Y, K379R, Q380R, A437G, A444T, E466K, D476H, P477D, K478D, A484C, A484Q, A484N, A484E, A484D, A484K, A484R, A484H, A484Y, and A484X (where X represents an unnatural amino acid, as described herein), E508R, D510K, D510R, K512Y, E515Q, K539E, D570S, and T571V (corresponding to positions in the reference F29 polymerase).

For example, in some embodiments, where a modified polymerase comprises a F29 polymerase majority sequence, the modified polymerase comprises one or more mutations at the positions as listed in the preceding. In some embodiments, where a modified polymerase does not comprise a F29 polymerase majority sequence, the modified polymerase comprises one or more amino acids that correspond to the positions listed above, e.g., as determined by homology alignment or other methods known in the art.

In some embodiments, a modified polymerase comprises mutations at one or more positions corresponding to Y148, Y226, V250, N251, T368, E375, K379, Q380, A437, P477, K478, and A484 in F29 polymerase. In some embodiments, a modified polymerase of the disclosure is a modified F29 polymerase comprising mutations at one or more of Y 148, Y226, V250, N251, T368, E375, K379, Q380, A437, P477, K478, and A484. In some embodiments, the modified polymerase comprises one or more of Y 1481, Y226F, V250A, N251R, T368F, E375K, K379R, Q380R, A437G, P477D, K478D, and A484C. In some embodiments, the modified polymerase comprises one or more of Y148I, Y226F, V250A, N251R, T368F, E375K, K379R, Q380R, A437G, P477D, K478D, and A484S. In some embodiments, the modified polymerase comprises one or more of Y 1481, Y226F, V250A, N251R, T368F, E375K, K379R, Q380R, A437G, P477D, K478D, and A484T. In some embodiments, the modified polymerase comprises one or more of Y148I, Y226F, V250A, N251R, T368F, E375K, K379R, Q380R, A437G, P477D, K478D, and A484Q. In some embodiments, the modified polymerase comprises one or more of Y148I, Y226F, V250A, N251R, T368F, E375K, K379R, Q380R, A437G, P477D, K478D, and A484N. In some embodiments, the modified polymerase comprises one or more of Y148I, Y226F, V250A, N251R, T368F, E375K, K379R, Q380R, A437G, P477D, K478D, and A484E. In some embodiments, the modified polymerase comprises one or more of Y148I, Y226F, V250A, N251R, T368F, E375K, K379R, Q380R, A437G,

P477D, K478D, and A484D. In some embodiments, the modified polymerase comprises one or more of Y148I, Y226F, V250A, N251R, T368F, E375K, K379R, Q380R, A437G, P477D, K478D, and A484K. In some embodiments, the modified polymerase comprises one or more of Y148I, Y226F, V250A, N251R, T368F, E375K, K379R, Q380R, A437G, P477D, K478D, and A484R. In some embodiments, the modified polymerase comprises one or more of Y 1481, Y226F, V250A, N251R, T368F, E375K, K379R, Q380R, A437G, P477D, K478D, and A484H. In some embodiments, the modified polymerase comprises one or more of Y 1481, Y226F, V250A, N251R, T368F, E375K, K379R, Q380R, A437G, P477D, K478D, and A484Y. In some embodiments, the modified polymerase comprises one or more of Y 1481, Y226F, V250A, N251R, T368F, E375K, K379R, Q380R, A437G, P477D, K478D, and A484X, where X represents an unnatural amino acid, as described herein. As used herein, one or more can be 2 or more, 4 or more, 6 or more, 8 or more, 10 or more, 12 or more, for example all, of the listed amino acid substitutions.

In some embodiments, a modified polymerase comprises mutations at one or more positions (e.g., at 1-35 positions or any whole number in between, for example 2 or more, 5 or more, 10 or more, 15 or more, 20 or more, for example all) corresponding to M8, V51, N62, 171, L107, K131, K135, L142, G197, Y224, E239, V250, L253, Y281, 1288, T301, R306, R308, D325, D341, K354, T368, E375, A437, A444, E466, D476, A484, E508, D510, K512, E515, K539, D570, and T571 in F29 polymerase. In some embodiments, a modified polymerase is a modified F29 polymerase comprising mutations at one or more of M8, V51, N62, 171, L107, K131, K135, L142, G197, Y224, E239, V250, L253, Y281, 1288, T301, R306, R308, D325, D341, K354, T368, E375, A437, A444, E466, D476, A484, E508, D510, K512, E515, K539, D570, and T571 in F29 polymerase. In some embodiments, the modified polymerase comprises one or more (e.g., 1-35 or any whole number in between, for example 2 or more, 5 or more, 10 or more, 15 or more, 20 or more, for example all) of the following mutations M8R, V51A, N62D,

17 IV, LI 071, K131E, K135Q, L142K, G197D, Y224K, E239G, V250A, V250I, L253A, L253H, Y281H, I288L, T301C, R306Q, R308L, D325E, D341E, K354R, T368F, E375Y, A437G, A444T, E466K, D476H, A484E, E508R, D510K, D510R, K512Y, E515Q, K539E, D570S, and T571V.

In some embodiments, a modified polymerase comprises mutations at one or more positions (e.g., at 1-18 positions or any whole number in between, for example 2 or more, 5 or more, 10 or more, 15 or more, for example all) corresponding to K135, L142, Y224, E239,

V250, L253, E375, A437, E466, D476, A484, E508, D510, K512, E515, K539, D570, and T571 in F29 polymerase. In some embodiments, a modified polymerase of the disclosure is a modified F29 polymerase comprising mutations at one or more of K135, L142, Y224, E239, V250, L253, E375, A437, E466, D476, A484, E508, D510, K512, E515, K539, D570, and T571. In some embodiments, the modified polymerase comprises one or more (e.g., 1-18 or any whole number in between, for example 2 or more, 5 or more, 10 or more, 15 or more, for example all) of K135Q, L142K, Y224K, E239G, V250I, L253A, E375Y, A437G, E466K, D476H, A484E, E508R, D510R, K512Y, E515Q, K539E, D570S, and T571V.

In some embodiments, a modified polymerase comprises mutations at one or more positions (e.g., 1, 2, or 3) corresponding to G197, 171, and L107 in F29 polymerase. In some embodiments, a modified polymerase of the disclosure is a modified F29 polymerase comprising mutations at one or more (e.g., 1, 2, or 3) of G197, 171, and L107. In some embodiments, the modified polymerase comprises one or more (e.g., 1, 2, or 3) of G197D, I71V, and L107I.

C. Domain, Subdomain, and Segment Modifications

As described above, modifications may comprise an addition, substitution, or deletion of one or more amino acids (which may or may not be consecutive), such as: (i) an addition, substitution, or deletion of an amino acid within a polymerase domain, subdomain, or segment; or (i) an addition, substitution, or deletion of a polymerase domain, subdomain, or segment.

FIG. 2, FIG. 9B, and FIG. 15 provide exemplary polymerase domains and subdomains. For example, FIG. 2 depicts a cartoon illustration of F29 polymerase 200. The folded, three- dimensional structure comprises distinct domains and subdomains corresponding to overlay 202: an N-terminal exonuclease domain (1) and a C-terminal polymerase domain that contains a palm subdomain (2), a terminal protein region 1 subdomain (TPR1) (3), a fingers subdomain (4), a TPR2 subdomain (5), and a thumb subdomain (6). These domains and subdomains map to areas of the polypeptide strand according to polypeptide construct 204, which is oriented in an N- terminal to C-terminal fashion. As shown, the N-terminal exonuclease domain (1) spans residues 1-189 and the C-terminal polymerase domain spans residues 190-575 of wild-type F29 polymerase. Within the C-terminal polymerase domain, the palm subdomain (2) spans residues 190-260 and 427-530, the TPR1 subdomain (3) spans residues 261-358, the fingers subdomain (4) spans residues 359-394, the TPR2 subdomain (5) spans residues 395-426, and the thumb subdomain (6) spans residues 531-575 of wild-type F29 polymerase.

A polymerase“segment,” as used herein, refers to a portion (e.g., at least 2 consecutive more amino acids) of a polymerase. In some embodiments, a segment comprises at least 2, at least 3, at least 4, at least 5, at least 10, at least 15, at least 20, at least 25, at least 30, at least 35, at least 40, at least 45, at least 50, at least 55, at least 60, at least 65, at least 70, at least 75, at least 80, at least 85, at least 90, at least 95, at least 100, at least 110, at least 120, at least 130, at least 140, at least 150, at least 160, at least 170, at least 180, at least 190, at least 200, at least 210, at least 220, at least 230, at least 240, at least 250, at least 275, or at least 300 consecutive amino acids of a polymerase. In some embodiments, a segment comprises 2, 3, 4, 5, 6, 7, 8, 9,

10, 11, 12, 13, 14, 15, 16, 17, 18, 9, 20, 21, 22, 23, 44, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35,

36, 37, 38, 9, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61,

62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87,

88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 105, 110, 115, 120, 125, 130, 140, or 150 consecutive amino acids of a polymerase. In some embodiments, a segment comprises a domain or a subdomain of a polymerase.

( i ) Modifications Within a Polymerase Domain, Subdomain, or Segment

In some embodiments, a recombinant polymerizing enzyme of the present application comprises one or more amino acid mutations in one or more domains, subdomains, or segments (optionally including flanking amino acids) of the polymerase. In some embodiments, the recombinant polymerizing enzyme comprises one or more amino acid mutations in one or more of an exonuclease region, a palm region, a TPR1 region, a fingers region, a TPR2 region, and a thumb region.

In some embodiments, a recombinant polymerizing enzyme comprises mutations at one or more positions in an exonuclease region (e.g., an exonuclease loop of an exonuclease region). In some embodiments, a recombinant polymerizing enzyme having an E. faecium polymerase majority sequence comprises mutations at one or more positions in an exonuclease region. For example, in some embodiments, a recombinant polymerizing enzyme of the disclosure is a modified E. faecium polymerase comprising mutations at one or more of (e.g., 2, 3, 4, 5, 6, 7, 8,

9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34,

35, or 36 of - in any combination) K4, T13, S22, V25, C26, D27, N33, 134, F36, S42, D54, N59, E60, E65, E85, M95, N106, T110, T114, K119, Q122, Y133, P136, E139, E142, N145, P147, 1148, E152, 1153, P160, D167, D171, N175, F188, and D189 in an exonuclease region of E. faecium polymerase. In some embodiments, a recombinant polymerizing enzyme comprises a mutation at one or more positions (e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, or 36 positions - in any combination) corresponding to K4, T13, S22, V25, C26, D27, N33, 134, F36, S42, D54, N59, E60, E65, E85, M95, N106, T110, T114, K119, Q122, Y133, P136, E139, E142, N145, P147, 1148, E152, 1153, P160, D167, D171, N175, F188, and D189 in E. faecium polymerase. Accordingly, in some embodiments, where a recombinant polymerizing enzyme does not comprise an E. faecium polymerase majority sequence, the recombinant polymerizing enzyme comprises one or more amino acids that correspond to the positions listed above, e.g., as determined by homology alignment or other methods known in the art. In some embodiments, the recombinant polymerizing enzyme comprises one or more of K4R, T13N, S22A, V25L, C26W, D27E, N33T, I34V, F36V, S42T, D54Y, N59D, E60L, E60V, E65S, E85P, M95T, M95K, N106G, T110I, T114S, K119Q, Q122V, Y133L, P136T, E139K, E139Q, E139R, E139H, E142K, E142Q, E142R, E142H, N145K, N145H, N145R, P147Q, P147T, I148K, I148H, I148R, E152D, I153V, P160A, D167P, D167K, D167H, D167R, D171K, D171H, D171R, N175T, N175Y, F188C, D189K, D189H, and D189R.

In some embodiments, a modified E. faecium polymerase of the disclosure comprises a modification that eliminates or reduces exonuclease activity. For example, in some

embodiments, the modified E. faecium polymerase comprises a mutation at N59 that eliminates or reduces exonuclease activity. In some embodiments, the modified E. faecium polymerase comprises N59D. In some embodiments, a modified E. faecium polymerase does not comprise a mutation at N59 (e.g., the modified E. faecium polymerase comprises N59). It should be appreciated that a mutation at N59 in a modified E. faecium polymerase can be introduced or reverted back to wild-type depending on a desired functionality. Accordingly, in some embodiments, a modified E. faecium polymerase comprises a sequence selected from TABLE 2, further modified to introduce a mutation at N59 (e.g., further modified to comprise N59D). In some embodiments, a modified E. faecium polymerase comprises a sequence selected from TABLE 2, further modified to revert a mutation at N59 back to wild-type (e.g., further modified to comprise D59N).

In some embodiments, a modified polymerase having a F29 polymerase majority sequence comprises mutations at one or more positions in an exonuclease region. For example, in some embodiments, a modified polymerase of the disclosure is a modified F29 polymerase comprising mutations at one or more of (e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10, or 11 of - in any combination) E75, R76, S82, A83, D84, G85, L86, P87, N88, Y90, and N91 in an exonuclease region of F29 polymerase. In some embodiments, a modified polymerase comprises one or more amino acid mutations at positions corresponding to E75, R76, S82, A83, D84, G85, L86, P87, N88, Y90, and N91 in F29 polymerase. Accordingly, in some embodiments, where a modified polymerase does not comprise a F29 polymerase majority sequence, the modified polymerase comprises one or more amino acids that correspond to the positions listed above, e.g., as determined by homology alignment or other methods known in the art. In some embodiments, the modified polymerase comprises one or more of E75F, R76K, S82C, A83K, D84E, G85A, L86K, P87E, N88R, Y90F, and N91S. Accordingly, in some embodiments, a segment comprising an exonuclease domain or portion thereof is swapped for a corresponding exonuclease domain from a different polymerase. For example, in some embodiments, a segment comprising a loop and flanking amino acids of an exonuclease domain of one polymerase are replaced with a corresponding segment from another polymerase. For example, in some embodiments, a F29 E75-N91 segment is replaced with a corresponding F72-S89 segment from E. faecium. In some embodiments, swapping a segment comprising an

exonuclease loop can reduce the interpulse distance of a polymerase.

In some embodiments, a modified polymerase comprises mutations at one or more positions in a TPR1 region. For example, in some embodiments, a modified polymerase comprises a mutation at one or more positions (e.g., 1, 2, 3, 4, 5, 6, or 7 - in any combination) corresponding to P273, P275, R308, V315, Q317, S319, L320, 1322, Q323, D337, E338, D341, T345, F352, F353, T364, and D374 in E. faecium polymerase. In some embodiments, a modified polymerase of the disclosure is a modified E. faecium polymerase comprising a mutation at one or more (e.g., 1, 2, 3, 4, 5, 6, or 7 - in any combination) of R308, S319, L320, E323, D337,

E338, and D341. In some embodiments, amino acids at one or more (e.g., 1, 2, 3, 4, 5, 6, or 7) of R308, S319, L320, E323, D337, E338, and D341 are changed to amino acids at corresponding positions in other polymerases (e.g., F29, M2Y, Lucilia cuprina, a Bacillus strain, for example GA-1). In some embodiments, the modified polymerase comprises one or more (e.g., 1, 2, 3, 4,

5, 6, or 7 - in any combination) of R308G, S319L, L320M, E323V, D337G, E338K, and D341T. In some embodiments, a modified polymerase comprises a mutation at one or more (e.g., 1, 2, 3, 4, 5, or 6 - in any combination) positions corresponding to Y281, 1288, T301, D325, D341, and K354 in F29 polymerase. In some embodiments, a modified polymerase of the disclosure is a modified F29 polymerase comprising mutations at one or more (e.g., 1, 2, 3, 4, 5, or 6 - in any combination) of Y281, 1288, T301, D325, D341, and K354. In some embodiments, amino acids at one or more (e.g., 1, 2, 3, 4, 5, or 6 - in any combination) of Y281, 1288, T301, D325, D341, and K354 are changed to amino acids at corresponding positions in other polymerases (e.g., M2Y, Lucilia cuprina , a Bacillus strain, for example GA-1). In some embodiments, the modified polymerase comprises one or more (e.g., 1, 2, 3, 4, 5, or 6 - in any combination) of Y281H, I288L, T301C, D325E, D341E, and K354R. In some embodiments, mutations at one or more (e.g., 1, 2, 3, 4, 5, or 6) positions corresponding to Y281, 1288, T301, D325, D341, and K354 in F29 polymerase increase rate of incorporation (e.g., in a single molecule sequencing reaction).

In some embodiments, a modified polymerase comprises a mutation at one or more positions in a palm region. For example, in some embodiments, a modified polymerase comprises a mutation at one or more (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, or 39 - in any combination) positions corresponding to Q206, T211, S216, R217, D232, A236, V247, 1253, V261, L264, S267, V443, L445, A446, S447, V449, T450, W452, G453, Y455, F465, N467, T479, E482, A484, E485, A486, L490, D492, S493, K495, K500, S503, Q506, Q513, E519,

D521, E523, and V526 in E. faecium polymerase. In some embodiments, a modified polymerase of the disclosure is a modified E. faecium polymerase comprising mutations at one or more (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29,

30, 31, 32, 33, 34, 35, 36, 37, 38, or 39 - in any combination) of T211, D232, V261, L264, T479, E482, D492, S493, K500, Q513, E519, D521, and E523. In some embodiments, amino acids at one or more (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, or 39 - in any combination) of T211, D232, V261, L264, T479, E482, D492, S493, K500, Q513, E519, D521, and E523 are changed to amino acids at corresponding positions in other polymerases (e.g., F29, M2Y, Lucilia cuprina, a Bacillus strain, for example GA-1). In some embodiments, a modification is selected from the group consisting of Q206R, Q206K, Q206H, T211A, S216G, S216R, R217G, D232K, A236G, V247D, I253H, I253A, V261A, V261I, V261L, L264H, L264A, L264M, V443T, L445M, A446G, S447V, V449I, T450A, W452Y, G453A, Y455W, F465Y, N467R, N467K, N467H, N467S, N467T, T479V, E482K, E482H, E482R, A484E, E485D, A486E, L490M, D492H, D492K, D492R, D492A, H492S, S493P, K495R, K500E, S503A, S503T, Q506K, Q513D, D521K, D521R, D521H, E523R, E523V, E523Y, E523F, E523H, E523W, and V526L.

In some embodiments, a modified polymerase comprises mutations at one or more (e.g.,

1, 2, 3, 4, or 5 - in any combination) positions corresponding to M429, G430, V431, 1433, and A444 in F29 polymerase. In some embodiments, a modified polymerase of the disclosure is a modified F29 polymerase comprising a mutation at one or more positions (e.g., 1, 2, 3, 4, or 5 - in any combination) of M429, G430, V431, 1433, and A444. In some embodiments, amino acids at one or more (e.g., 1, 2, 3, 4, or 5 - in any combination) of M429, G430, V431, 1433, and A444 are changed to amino acids at corresponding positions in other polymerases (e.g., M2Y, Lucilia cuprina, a Bacillus strain, for example GA-1). In some embodiments, the modified polymerase comprises one or more (e.g., 1, 2, 3, 4, or 5 - in any combination) of M429L, G430A, V431S, I433V, and A444T. In some embodiments, mutations at one or more (e.g., 1, 2, 3, 4, or 5 - in any combination) positions corresponding to M429, G430, V431, 1433, and A444 in F29 polymerase increase accuracy (e.g., in a single molecule sequencing reaction).

In some embodiments, a modified polymerase comprises mutations at one or more positions in a fingers region. For example, in some embodiments, a modified polymerase comprises mutations at one or more (e.g., 1, 2, 3, 4, 5, 6, or 7 - in any combination) positions corresponding to 1384, E385, N388, E391, A396, N397, and G400 in E. faecium polymerase. In some embodiments, a modified polymerase of the disclosure is a modified E. faecium

polymerase comprising mutations at one or more (e.g., 1, 2, 3, 4, 5, 6, or 7 - in any combination) positions corresponding to 1384, E385, N388, E391, A396, N397, and G400 in E. faecium polymerase. In some embodiments, the mutation is selected from the group consisting of I384T, I384F, I384S, E385Y, E385K, E385R, E385N, E385Q, E385L, E385A, N388T, E391Y, E391W, E391F, E391H, E391M, E391K, E391R, A396Q, N397L, and G400L. In some embodiments, amino acids at one or more (e.g., 1, 2,3, 4, 5, 6, or 7 - in any combination) positions

corresponding to 1384, E385, N388, E391, A396, N397, and G400 are changed to amino acids at corresponding positions in other polymerases (e.g., F29, M2Y, Lucilia cuprina , a Bacillus strain, for example GA-1).

In some embodiments, a modified polymerase comprises a mutation at one or more positions in a TPR2 region. For example, in some embodiments, a modified polymerase comprises a mutation at one or more positions (e.g., 1, 2, 3, 4, or 5 - in any combination) corresponding to D414, D425, R429, E436, and F437 in E. faecium polymerase. In some embodiments, a modified polymerase of the disclosure is a modified E. faecium polymerase comprising a mutation at one or more (e.g., 1, 2, 3, 4, or 5 - in any combination) of D414, D425, R429, E436, and L437. In some embodiments, the mutation is selected from the group consisting of D414V, D425N, R429G, E436R, E436G, L437Y, and L437E. In some

embodiments, an amino acid at the position corresponding to D414, D425, R429, E436, or L437 is changed to an amino acid at a corresponding position in other polymerases (e.g., F29, M2Y, Lucilia cuprina, a Bacillus strain, for example GA-1).

In some embodiments, a modified polymerase comprises a mutation at one or more positions in a thumb region. For example, in some embodiments, a modified polymerase comprises a mutation at one or more positions (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or 13 - in any combination) corresponding to D533, R534, E537, G547, E545, L555, P556, R558, T559, V564, T568, M569, and T571 in E. faecium polymerase. In some embodiments, a modified polymerase of the disclosure is a modified E. faecium polymerase comprising mutations at one or more (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or 13 - in any combination) of D533, R534, E537, G547, E545, L555, P556, R558, T559, V564, T568, M569, and T571. In some embodiments, a mutation is selected from the group consisting of D533A, D533Q, D533T, D533R, D533S, R534K, E537K, E537H, E537R, E545K, E545H, E545R, G547S, L555K, L555R, P556A, R558H, T559V, V564L, T568D, T568S, M569K, M569T, M569V, and T571S. In some embodiments, amino acids at one or more (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or 13 - in any combination) positions corresponding to D533, R534, E537, G547, E545, L555, P556, R558, T559, V564, T568, M569, and T571 are changed to amino acids at corresponding positions in other polymerases (e.g., F29, M2Y, Lucilia cuprina , a Bacillus strain, for example GA-1).

In some embodiments, a modified polymerase comprises mutations at one or more positions in a palm region and at one or more positions in an exonuclease region. For example, in some embodiments, a modified polymerase comprises mutations at one or more (e.g., 1, 2, or 3) positions corresponding to G197, M8, and V51 in F29 polymerase. In some embodiments, a modified polymerase of the disclosure is a modified F29 polymerase comprising mutations at one or more (e.g., 1, 2, or 3) of G197, M8, and V51. In some embodiments, the modified polymerase comprises one or more (e.g., 1, 2, or 3) of G197D, M8R, and V51A. In some embodiments, mutations at one or more (e.g., 1, 2, or 3) positions corresponding to G197, M8, and V51 in F29 polymerase can improve production yield, thermostability, and/or improve efficiency of loading (e.g., loading into sample wells of an array).

In some embodiments, a modified polymerase comprises mutations at one or more positions in a palm region and at one or more positions in a thumb region. For example, in some embodiments, a modified polymerase comprises mutations at one or more (e.g., 1, 2, 3, 4, or 5) positions corresponding to E466, D476, K539, D570, and T571 in F29 polymerase. In some embodiments, a modified polymerase of the disclosure is a modified F29 polymerase comprising mutations at one or more (e.g., 1, 2, 3, 4, or 5) of E466, D476, K539, D570, and T571. In some embodiments, the modified polymerase comprises one or more (e.g., 1, 2, 3, 4, or 5) of E466K, D476H, K539E, D570S, and T571V.

In some embodiments, a modified polymerase comprises one or more (e.g., 1, 2, 3, 4, 5,

6, or 7) amino acid mutations at positions corresponding to N59, Y145, V247, L250, E372,

A481, and K509 in M2Y polymerase. For example, in some embodiments, where a modified polymerase comprises an M2Y polymerase majority sequence, the modified polymerase comprises one or more mutations at the positions as listed in the preceding. In some

embodiments, where a modified polymerase does not comprise an M2Y polymerase majority sequence, the modified polymerase comprises one or more amino acid mutations that correspond to the positions listed above, e.g., as determined by homology alignment or other methods known in the art.

In some embodiments, a modified polymerase comprises one or more segments (e.g., domains or portions thereof, optionally including flanking amino acids) of a wild-type polymerase (e.g., as set forth in TABLE 1, e.g., SEQ ID NO: 1, SEQ ID Nos: 2-5, or SEQ ID Nos: 23-33). In some embodiments, one or more segments (e.g., domains or portions thereof, optionally including flanking amino acids) of an Enterococcus faecium polymerase (e.g., one or more segments of any one of SEQ ID NOs: 2-5) can be substituted for one or more segments of any one of SEQ ID NOs: 1 and 6-33. In some embodiments, one or more segments (e.g., domains or portions thereof, optionally including flanking amino acids) of an Enterococcus faecium polymerase (e.g., one or more segments of any one of SEQ ID NOs: 2-5) can be substituted for one or more segments of any one of SEQ ID NOs: 23-33. In some embodiments, one or more segments (e.g., domains or portions thereof, optionally including flanking amino acids) of an Enterococcus faecium polymerase can be substituted for one or more segments of a F29 polymerase. In some embodiments, one or more segments (e.g., domains or portions thereof, optionally including flanking amino acids) of an Enterococcus faecium polymerase can be substituted for one or more segments of an M2Y polymerase. In some embodiments, one or more segments (e.g., domains or portions thereof, optionally including flanking amino acids) of an Enterococcus faecium polymerase can be substituted for one or more segments of a F29 polymerase and/or an M2Y polymerase. In some embodiments, one or more segments (e.g., domains or portions thereof, optionally including flanking amino acids) of an Enterococcus faecium polymerase (e.g., a domain of any one of SEQ ID NOs: 2-5 or a modified form thereof, e.g., containing one or more amino acid substitutions) can be substituted for one or more segments of a variant polymerase described herein (e.g., of a variant polymerase listed in

TABLE 3, or a variant polymerase containing one or more amino acid substitutions or other domain substitutions illustrated in TABLE 3 or described in TABLES 4-6).

(ii) Modifications Of a Polymerase Domain, Subdomain, or Segment - Chimeric Polymerases

FIG. 2 depicts a cartoon illustration of F29 polymerase 200. The folded, three- dimensional structure comprises distinct domains and subdomains corresponding to overlay 202: an N-terminal exonuclease domain (1) and a C-terminal polymerase domain that contains a palm subdomain (2), a terminal protein region 1 subdomain (TPR1) (3), a fingers subdomain (4), a TPR2 subdomain (5), and a thumb subdomain (6). These domains and subdomains map to areas of the polypeptide strand according to polypeptide construct 204, which is oriented in an N- terminal to C-terminal fashion. As shown, the N-terminal exonuclease domain (1) spans residues 1-189 and the C-terminal polymerase domain spans residues 190-575 of wild-type F29 polymerase. Within the C-terminal polymerase domain, the palm subdomain (2) spans residues 190-260 and 427-530, the TPR1 subdomain (3) spans residues 261-358, the fingers subdomain (4) spans residues 359-394, the TPR2 subdomain (5) spans residues 395-426, and the thumb subdomain (6) spans residues 531-575 of wild-type F29 polymerase. Equivalent segments (e.g., domains or portions thereof, optionally including flanking amino acids) of different polymerases described in this application can be substituted for each other to produce chimeric polymerases. For example, one or more of an exonuclease domain, a palm subdomain, a TPR1 subdomain, one or more finger subdomains, a TPR2 subdomain, and/or a thumb subdomain from one polymerase (e.g., having a wild type sequence shown in TABLE 1 or having one or more mutations exemplified in TABLES 2-3 or described in TABLES 4-6) can be substituted for a corresponding domain in another polymerase (e.g., having a wild type sequence shown in TABLE 1 or having one or more mutations exemplified in TABLES 2-3 or described in TABLES 4-6). In some embodiments, segments comprising portions of one or more of these domains, optionally including one or more flanking amino acids, can be substituted.

In some embodiment, a modification of a polymerase comprises an addition of a segment, subdomain, or domain. For example, in some embodiments, a modification comprises a duplication of a segment, subdomain, or domain of a polymerase. In some embodiment, a modification comprises an addition of a segment, subdomain, or domain of a reference polymerase (thereby producing a“chimeric polymerase” as described herein). In some embodiments, a modification of a polymerase comprises an addition of a non-native chemical entity. For example, in some embodiments, a modification of a polymerase comprises the addition of one or more histidine residues at the N-terminus of a polymerase. In some embodiments, a modification of a polymerase comprises the addition of a bis-biotin tag.

In some embodiments, a modification of a polymerase comprises a deletion of a segment, subdomain, or domain.

In some embodiments, a modification of a polymerase comprises a substitution of a segment, subdomain, or domain with a corresponding domain of a reference polymerase (thereby producing a“chimeric polymerase” as described herein, see e.g., FIG. 6). For example, one or more of an exonuclease domain, a palm subdomain, a TPR1 subdomain, one or more finger subdomains, a TPR2 subdomain, and/or a thumb subdomain from one polymerase (e.g., having a wild type sequence shown in TABLE 1 or having one or more mutations exemplified herein) can be substituted for a corresponding domain in another polymerase (e.g., having a wild type sequence shown in TABLE 1 or having one or more mutations exemplified herein). In some embodiments, segments comprising portions of one or more of these domains, optionally including one or more flanking amino acids, can be substituted.

For example, in some embodiments, a modified polymerase comprises a TPR1 region substitution. For example, in some embodiments, a modified polymerase comprises a TPR1 region from E. faecium (e.g., V271-M375 in SEQ ID NO: 5) in place of a TPR1 region corresponding to S260-L359 in F29 polymerase (SEQ ID NO: 1).

In some embodiments, a modified polymerase of the present application comprises one or more substitutions within an exonuclease region. For example, in some embodiments, a modified polymerase comprises a portion of an exonuclease region from M2Y (e.g., MI-151 in SEQ ID NO: 6) in place of amino acids corresponding to M1-V54 in F29 polymerase (SEQ ID NO: 1). In some embodiments, a modified polymerase comprises a portion of an exonuclease region from E. faecium (e.g., F72-S89 in SEQ ID NO: 2) in place of amino acids corresponding to E75-N91 in F29 polymerase (SEQ ID NO: 1). In some embodiments, a modified polymerase comprises the portion of the exonuclease region from M2Y and the portion of the exonuclease region from E. faecium in place of amino acids corresponding to M1-V54 and E75-N91, respectively, in F29 polymerase.

In some embodiments, a modified polymerase of the present application comprises a modified palm region. For example, in some embodiments, a modified polymerase comprises a portion of a palm region from E. faecium (e.g., L445-V449 in SEQ ID NO: 2) in place of amino acids corresponding to M429-I433 in F29 polymerase (SEQ ID NO: 1). In some embodiments, a modified polymerase comprises an alanine to thymine mutation at a position corresponding to A444 in F29 polymerase (e.g., A444T). In some embodiments, a modified polymerase comprises the portion of the palm region from E. faecium and an amino acid mutation

corresponding to A444T in F29 polymerase.

In some embodiments, a modified polymerase comprises a majority polymerase sequence other than F29 polymerase. In such embodiments, the majority polymerase sequence comprises one or more regions that may be analogized to F29 polymerase 200 (e.g., based on homology alignment, computational modeling, structural analysis, or any suitable method). As used herein, a“region” of a polymerase refers to a distinct domain or subdomain of a polymerase enzyme.

For example, in some embodiments, a region of a polymerase refers to an N-terminal

exonuclease domain or a C-terminal polymerase domain. In some embodiments, a region of a polymerase refers to a palm subdomain, a TPR1 subdomain, a fingers subdomain, a TPR2 subdomain, or a thumb subdomain. Accordingly, in some embodiments, a region of a polymerase refers to all amino acids that comprise a given domain or subdomain. In some embodiments, a modified polymerase comprises modifications to one or more regions of a majority polymerase sequence. In some embodiments, a modified polymerase comprises modifications to one or more portions of a majority polymerase sequence. As used herein, a “portion” of a polymerase refers to a stretch of two or more consecutive residues within the polymerase sequence. In some embodiments, a portion of a polymerase sequence refers to two or more consecutive amino acids in a single polymerase domain or a single polymerase subdomain. In some embodiments, a portion of a polymerase sequence refers to two or more consecutive amino acids spanning more than one polymerase domain and/or subdomain. Thus, in some embodiments, a portion of a polymerase sequence is any stretch of consecutive amino acids within the polymerase sequence. In some embodiments, a portion refers to 5-10 consecutive amino acids, 10-25 consecutive amino acids, 25-50 consecutive amino acids, 50-75 consecutive amino acids, 75-100 consecutive amino acids or other number of consecutive amino acids that constitute a portion of, for example, a polymerase region or domain.

In some embodiments, a modified polymerase comprises one or more single-site mutations in one or more of the domains and/or subdomains as generally depicted in FIG. 2. For example, FIG. 3 depicts selected mutational variants of TABLE 3 with sites of mutation (shown approximated with arrows) within each polypeptide strand. Polypeptide strands are shown for M2Y and M2Y mutational variant HO 16, Lucilia cuprina and Lucilia cuprina mutational variant HO 18, Enterococcus faecium and Enterococcus faecium mutational variant H020, and Bacillus phage VMY22 and Bacillus phage VMY22 mutational variant H022. However, chimeras comprising other segment swaps and/or amino acid mutations as described herein also can be used.

In some embodiments, in addition or alternative to the one or more single-site mutational modifications described herein, a stretch of amino acids (e.g., two or more consecutive amino acids) in a majority polymerase sequence are modified. In some embodiments, the stretch of amino acids is a stretch of amino acids corresponding to a portion of a different polymerase sequence. For example, in some embodiments, a domain/subdomain (or a portion therein) of a majority polymerase sequence is swapped with a corresponding domain/subdomain (or portion therein) of a different polymerase sequence. In such embodiments, the polymerase is referred to as a chimeric polymerase, chimeric polymerase variant, or a chimera. Chimeric polymerases were engineered in accordance with embodiments described herein and are listed in TABLE 4.

In some embodiments, a modified recombinant polymerase enzyme of the disclosure is selected from TABLE 4. In some embodiments, a chimeric polymerase variant (e.g., as listed in TABLE 4) comprises a majority polymerase sequence having a region or portion of the majority sequence substituted with a corresponding region or portion of a different polymerase sequence. In some embodiments, all of the residues that comprise a region (e.g., domain and/or subdomain) in a majority polymerase sequence are substituted with all of the residues that comprise a corresponding region in a different polymerase sequence. In some embodiments, at least a portion of the residues that comprise a region in a majority polymerase sequence are substituted with at least a portion of the residues that comprise a corresponding region in a different polymerase sequence.

In some embodiments, only a single subdomain in a majority sequence is substituted with a corresponding subdomain of a different sequence. For example, FIG. 4 depicts chimeric polymerase variants selected from TABLE 4. The six selected variants are shown as polypeptide strands with subdomains as they generally occur within a polypeptide in an amino-terminal to carboxy-terminal orientation. Each of the polypeptide strands of FIG. 4 comprise a polymerase majority sequence of Q001 (hatched fill), with one or more domains and/or subdomains substituted with one or more corresponding domains and/or subdomains of M2Y polymerase (SEQ ID NO: 6, open fill) or one or more corresponding domains and/or subdomains of Lucilia cuprina (SEQ ID NO: 7, stippled fill) and or one or more flanking amino acids.

In some embodiments, a chimeric polymerase variant comprises a majority polymerase sequence having an exonuclease domain substituted from a different polymerase sequence. As shown in FIG. 4, C017 is a chimeric polymerase variant that comprises an exonuclease domain substituted from an M2Y polymerase sequence (e.g., as set forth in SEQ ID NO: 6). Similarly, C020 comprises an exonuclease domain substituted from a Lucilia cuprina polymerase sequence (e.g., as set forth in SEQ ID NO: 7). In some embodiments, modification or replacement of an exonuclease domain in a modified polymerase variant may be useful where proofreading capabilities of the polymerase are not desirable (e.g., in sequencing reactions). However, it should be appreciated that additional and alternative domain and/or subdomain substitutions are contemplated for the modified recombinant polymerases of the disclosure.

In some embodiments, a chimeric polymerase variant comprises a majority polymerase sequence having an exonuclease loop substituted from a different polymerase sequence. As used herein, in some embodiments, an“exonuclease loop” refers to a stretch of consecutive amino acids that forms a loop region in an exonuclease domain. For example, FIG. 5A depicts a cartoon illustration of F29 polymerase in full perspective 500 and zoomed perspective 502. Zoomed perspective 502, a close-up view of the boxed area shown in full perspective 500, shows a loop region in the exonuclease domain of F29 polymerase. Selected loop residues are shown in stick form in zoomed perspective 502, with the stretch of consecutive amino acids that form the exonuclease loop spanning residues N77 through N88. Evolutionary conservation analysis of this region of the exonuclease domain revealed that the loop, and several flanking residues, is relatively poorly conserved. FIG. 5B depicts a homology alignment 504 between exonuclease regions of F29 polymerase and a non-limiting set of other polymerases selected from TABFE 1. Also depicted is a loop homology alignment 506 showing exonuclease loop N77-N88 of F29 polymerase and the corresponding exonuclease loop in other polymerases.

Based on the homology analysis showing relatively low conservation in regions corresponding to exonuclease loop N77-N88 of F29 polymerase, this provided a source of variation in the search for desirable biochemical properties in a polymerase variant (e.g., desirable for use in sequencing reactions). Accordingly, in some embodiments, a chimeric polymerase variant comprises a majority polymerase sequence having an exonuclease loop substituted from a different polymerase sequence, where an“exonuclease loop” is homologous to exonuclease loop N77- N88 of F29 polymerase (e.g., as shown by loop homology alignment 506 in FIG. 5B).

As shown by the example alignment in FIG. 5B, sequence homology analysis can be used to identify an exonuclease loop sequence that is homologous to N77-N88 of F29 polymerase.

By way of example and not limitation, the loop homology alignment 506 shows homologous exonuclease loop sequences for M2Y (H74-N85), Lucilia cuprina (N64-G76), E. faecium (N74- R86), Bacillus GA-1 (N74-K88), Bacillus VMY22 (K80-K91 ), Actinomyces AV-1 (H93-K105), Potato cyst nematode (F86-K99), Iberian lynx gut (D73-R87), Candidatus (N85-N98), and Eggerthella sp. (V73-K88). Accordingly, in some embodiments, a substituted exonuclease loop can include between around 12 and around 16 amino acids in a region of homology to N77-N88 of F29 polymerase. In some embodiments, a substituted exonuclease loop comprises between around 10 amino acids and up to 20 amino acids, between around 5 amino acids and up to 15 amino acids, between around 5 amino acids and up to 20 amino acids, or between around 5 amino acids and 25 amino acids or more, in a region of homology to N77-N88 of F29 polymerase.

In some embodiments, a modified polymerase of the present application comprises one or more amino acid mutations in a region of an exonuclease domain that includes an exonuclease loop of homology to N77-N88 of F29 polymerase. For example, in some embodiments, a modified polymerase of the disclosure is a modified F29 polymerase comprising mutations at one or more of E75, R76, S82, A83, D84, G85, L86, P87, N88, Y90, and N91 in F29

polymerase. In some embodiments, the modified polymerase comprises one or more of E75F, R76K, S82C, A83K, D84E, G85A, L86K, P87E, N88R, Y90F, and N91S. In some

embodiments, a modified polymerase comprises one or more amino acid mutations at positions corresponding to E75, R76, S82, A83, D84, G85, L86, P87, N88, Y90, and N91 in F29 polymerase. For example, in some embodiments, where a modified polymerase does not comprise a F29 polymerase majority sequence, the modified polymerase comprises one or more amino acids that correspond to the positions listed above, e.g., as determined by homology alignment or other methods known in the art.

In some embodiments, a chimeric polymerase variant comprises a majority polymerase sequence having a TPR1 subdomain substituted from a different polymerase sequence. For example, C018 is a chimeric polymerase that comprises a TPR1 subdomain substituted from an M2Y polymerase sequence. Similarly, C021 comprises a TPR1 subdomain substituted from a Lucilia cuprina polymerase. In some embodiments, a chimeric polymerase variant comprises a majority polymerase sequence having a palm subdomain substituted from a different polymerase sequence. In some embodiments, a chimeric polymerase variant comprises a majority polymerase sequence having a fingers subdomain substituted from a different polymerase sequence. In some embodiments, a chimeric polymerase variant comprises a majority polymerase sequence having a TPR2 subdomain substituted from a different polymerase sequence. In some embodiments, a chimeric polymerase variant comprises a majority polymerase sequence having a thumb subdomain substituted from a different polymerase sequence. As described herein, modified recombinant polymerases include chimeric polymerase variants comprising more than one domain and/or subdomain substitution. In some embodiments, two regions (e.g., domains/subdomains) in a majority sequence are substituted with two corresponding regions (e.g., corresponding domains/subdomains) of a different sequence. For example, as shown in FIG. 4, C019 is a chimeric polymerase that comprises an exonuclease domain and TPR1 subdomain substituted with corresponding exonuclease domain and TPR1 subdomain of an M2Y polymerase sequence. Similarly, C022 comprises exonuclease domain and TPR1 subdomain substituted with corresponding

exonuclease domain and TPR1 subdomain of a Lucilia cuprina polymerase. In some

embodiments, additional domain and/or subdomain substitutions are contemplated with the modified polymerases described herein. For example, in some embodiments, more than two (e.g., three, four, five, or six) regions (e.g., domains/subdomains) in a majority sequence are substituted with more than two (e.g., three, four, five, or six) corresponding regions of a different sequence.

In some embodiments, a majority polymerase sequence of a chimeric polymerase variant is selected from a sequence in TABLES 1-4. In some embodiments, a majority polymerase sequence of a chimeric polymerase variant is selected from SEQ ID Nos: 2-5, or SEQ ID Nos: 23-33. In some embodiments, the majority polymerase sequence comprises one or more regions and/or portions substituted from a different polymerase sequence selected from TABLES 1-4.

For example, TABLE 5 provides an overview of selected chimeric polymerase variants from TABLE 4 and lists a majority polymerase sequence for each along with a description of the substituted region(s)/portion(s) and the sequence from which the substitution was based.

However, other chimeras, for example as described and illustrated in one or more of the Tables herein can be used and/or further modified.

In some embodiments, a chimeric polymerase variant may further comprise one or more site-specific mutations. Thus, in some embodiments, any of the one or more mutations described herein (e.g., any of the one or more mutations included in each sequence in Tables 2-3) may be applied to any of the chimeric polymerases contemplated in the present disclosure (e.g., as described in the above and listed in TABLE 4). FIG. 6 generally depicts chimeric polymerase variants comprising one or more mutations. For example, mutant chimeric polymerase 602 comprises a F29 polymerase majority sequence having a substituted M2Y exonuclease domain and mutations within the substituted domain. In some embodiments, a mutant chimeric polymerase comprises a majority sequence with two or more regions substituted with regions corresponding to two or more different polymerase sequences. For example, mutant chimeric polymerase 604 comprises a F29 polymerase majority sequence having a substituted

Enterococcus faecium polymerase TPR1 subdomain and a substituted M2Y polymerase TPR2 subdomain, with site-specific mutations made at various positions in the polymerase sequence.

In some embodiments, a mutant chimeric polymerase comprises a majority sequence with two or more regions substituted with regions corresponding to a different polymerase. For example, mutant chimeric polymerase 606 comprises a F29 polymerase majority sequence having substituted Enterococcus faecium polymerase TPR1, TPR2, and thumb subdomains, with site- specific mutations made at various positions in the polymerase sequence

TABLE 6 provides an overview of selected chimeric polymerase variants from TABLE 4, which provides a majority polymerase sequence for each along with a description of the amino acid mutations made to the particular variant.

However, other amino acid mutations can be incorporated into one or more chimeric polymerases described herein. For example, one or more amino acids changes can be incorporated at one or more of positions M8, V51, N62, 171, L107, and/or K131, and/or at one or more of positions K135, L142, G197, Y224, E239, V250, L253, Y281, 1288, T301, R306, R308, D325, D341, K354, T368, E375, A437, A444, E466, D476, A484, E508, D510, K512, E515, K539, D570, and T571 with reference to the F29 polymerase sequence. For example, in some embodiments, a chimeric polymerase also may include one or more of the following amino acid substitutions: M8R, V51A, N62D, 17 IV, L107I, and/or K131E, and/or one or more of the following amino acid substitutions: K135Q, L142K, G197D, Y224K, E239G, V250A, V250I, L253A, L253H, Y281H, I288L, T301C, R306Q, R308L, D325E, D341E, K354R, T368F, E375Y, A437G, A444T, E466K, D476H, A484E, E508R, D510K, D510R, K512Y, E515Q, K539E, D570S, and/or T571V.

In other embodiments, one or more amino acids changes can be incorporated at one or more of positions K4, T13, S22, V25, C26, D27, N33, 134, F36, S42, D54, N59, E60, E65, E85, M95, N106, T110, T114, K119, Q122, Y133, P136, E139, E142, N145, P147, 1148, E152, 1153, PI 60, D167, D171, N175, F188, D189, Q206, T211, S216, R217, D232, A236, V247, 1253, V261, L264, S267, P273, P275, R308, V315, Q317, S319, L320, 1322, Q323, D337, E338,

D341, T345, F352, F353, T364, D374, 1384, E385, N388, E391, A396, N397, G400, D414, D425, R429, E436, L437, V443, L445, A446, S447, V449, T450, W452, G453, Y455, F465, N467, T479, E482, A484, E485, A486, L490, D492, S493, K495, K500, S503, Q506, Q513, E519, D521, E523, V526, D533, R534, E537, G547, E545, L555, P556, R558, T559, V564, T568, M569, and/or T571 with reference to E. faecium polymerase (SEQ ID NO: 2). In some embodiments, a chimeric polymerase also may include one or more of the following amino acid substitutions: K4R, T13N, S22A, V25L, C26W, D27E, N33T, I34V, F36V, S42T, D54Y, N59D, E60L, E60V, E65S, E85P, M95T, M95K, N106G, T110I, T114S, K119Q, Q122V, Y133L, P136T, E139K, E139Q, E139R, E139H, E142K, E142Q, E142R, E142H, N145K, N145H, N145R, P147Q, P147T, I148K, I148H, I148R, E152D, I153V, P160A, D167P, D167K, D167H, D167R, D171K, D171H, D171R, N175T, N175Y, F188C, D189K, D189H, D189R, Q206R, Q206K, Q206H, T211A, S216G, S216R, R217G, D232K, A236G, V247D, I253H, I253A, V261A, V261I, V261L, L264H, L264A, L264M, S267A, P273S, P273R, P275S, E283K,

V315L, S319R, R308G, G308R, Q317R, S319R, L320M, L320T, I322K, Q323G, Q323V, Q323R, D337G, E338K, D341T, T345I, F352I, F353C, T364I, D374G, D374Q, D374H, I384T, I384F, I384S, E385Y, E385K, E385R, E385N, E385Q, E385L, E385A, N388T, E391Y, E391W, E391F, E391H, E391M, E391K, E391R, A396Q, N397L, G400L, D414V, D425N, R429G, E436R, E436G, L437Y, L437E, V443T, L445M, A446G, S447V, V449I, T450A, W452Y,

G453A, Y455W, F465Y, N467R, N467K, N467H, N467S, N467T, T479V, E482K, E482H, E482R, A484E, E485D, A486E, L490M, D492H, D492K, D492R, D492A, H492S, S493P, K495R, K500E, S503A, S503T, Q506K, Q513D, D521K, D521R, D521H, E523R, E523V, E523Y, E523F, E523H, E523W, V526L, D533A, D533Q, D533T, D533R, D533S, R534K, E537K, E537H, E537R, E545K, E545H, E545R, G547S, L555K, L555R, P556A, R558H,

T559V, V564L, T568D, T568S, M569K, M569T, M569V, and/or T571S.

TABLE 2. E. faecium polymerase variants

TABLE 3. Homologous Polymerase Variants

TABLE 4. Chimeric Polymerase Variants

TABLE 5. Chimeric Polymerases - Substituted Portions

TABLE 6. Chimeric Polymerases - Site-Specific Mutants

TABLE 7. Exemplary modification combinations - positions corresponding to SEQ ID NO: 2.

II. Compositions and Kits Comprising A Modified Recombinant Enzyme In some aspects, the disclosure relates to compositions comprising a modified polymerase described herein. In some embodiments, a composition comprises a plurality of modified polymerases. In some embodiments, the composition further comprises a salt and/or buffer.

In some aspects, the disclosure relates to kits comprising a modified polymerase described herein. In some embodiments, a kit comprises a plurality of modified polymerases.

Kits optionally may provide additional components such as buffers and interpretive information. Normally, the kit comprises a container and a label or package insert(s) on or associated with the container. In some embodiment, the disclosure provides articles of manufacture comprising contents of the kits described above. Suitable packaging includes, but is not limited to, vials, bottles, jars, flexible packaging, and the like. In some embodiments, the kit further comprises a container, a salt, and/or a buffer.

III. Methods of Producing a Modified Recombinant Enzyme

In some aspects, the disclosure relates to methods of recombinantly producing a modified polymerase described herein. In some embodiments, to express a polymerase of the disclosure, DNA encoding the polymerase is inserted into one or more expression vectors such that the encoded polymerase is operatively linked to transcriptional and translational control sequences (see, e.g., U.S. Pat. No. 6,914,128, the contents of which is incorporated herein by reference). In this context, the term“operatively linked” is intended to mean that a sequence encoding the polymerase is ligated into a vector such that transcriptional and translational control sequences within the vector serve their intended function of regulating the transcription and translation of the polymerase. The expression vector and expression control sequences are chosen to be compatible with the expression host cell used. Polymerase-encoding sequences are inserted into expression vectors by standard methods (e.g., ligation of complementary restriction sites on the polymerase-encoding sequence and vector or blunt end ligation if no restriction sites are present).

For expression of a modified polymerase, an expression vector encoding the modified polymerase can be transfected into a host cell by standard techniques. The various forms of the term“transfection” are intended to encompass a wide variety of techniques commonly used for the introduction of exogenous DNA into a prokaryotic or eukaryotic host cell, e.g.,

electroporation, calcium-phosphate precipitation, DEAE-dextran transfection, and the like.

Suitable host cells for expressing a polymerase of the disclosure include prokaryote, yeast, or higher eukaryote cells.

Suitable prokaryotes for this purpose include eubacteria, such as Gram-negative or Gram positive organisms, e.g., Enterobacteriaceae such as Escherichia, e.g., E. coli, Enterobacter, Erwinia, Klebsiella, Proteus, Salmonella, e.g., Salmonella typhimurium, Serratia, e.g., Serratia marcescans, and Shigella, as well as Bacilli such as B. subtilis and B. licheniformis,

Pseudomonas such as P. aeruginosa, and Streptomyces. In addition to prokaryotes, eukaryotic microbes such as filamentous fungi or yeast are suitable cloning or expression hosts for polypeptide encoding vectors. Saccharomyces cerevisiae, or common baker’s yeast, is the most commonly used among lower eukaryotic host microorganisms. However, a number of other genera, species, and strains are commonly available and useful herein, such as

Schizosaccharomyces pombe Kluyveromyces hosts such as, e.g., K. lactis, K. fragilis, K.

bulgaricus, K. wickeramii, K. waltii, K. drosophilarum, K. thermotolerans , and K. marxianus, Pichia pastoris, Candida, Trichoderma reesia, Neurospora crassa ; Schwanniomyces such as Schwanniomyces occidentalis, and filamentous fungi such as, e.g., Neurospora, Penicillium, Tolypocladium, and Aspergillus hosts such as A. nidulans and A. niger.

In some embodiments, host cells are transformed with the above-described expression or cloning vectors for polymerase production and cultured in conventional nutrient media modified as appropriate for inducing promoters, selecting transformants, or amplifying the genes encoding the desired sequences. The host cells used to produce a polymerase may be cultured in a variety of media. Commercially available media such as Ham’s F10™ (Sigma), Minimal Essential Medium™ (MEM), (Sigma), RPMI-1640 (Sigma), and Dulbecco's Modified Eagle's Medium™ (DMEM), (Sigma) are suitable for culturing the host cells. The culture conditions, such as temperature, pH, and the like, are those previously used with the host cell selected for expression, and will be apparent to the ordinarily skilled artisan.

In some embodiments, a polymerase variant can be produced intracellularly, in the periplasmic space, or directly secreted into the medium of a cell. In embodiments where the polymerase variant is produced intracellularly, the particulate debris, either host cells or lysed cells (e.g., resulting from homogenization), can be removed by a variety of means, including but not limited to, by centrifugation or ultrafiltration. Where the polymerase is secreted into the medium, supernatants from such expression systems can be first concentrated using a commercially available protein concentration filter, which can then be subjected to one or more additional purification techniques, including but not limited to affinity chromatography, including protein affinity chromatography, ion exchange chromatography, such as anion or cation exchange chromatography, and hydrophobic interaction chromatography.

In some embodiments, a modified polymerase comprises one or more unnatural amino acid substitutions. As used herein, an“unnatural amino acid” refers to any amino acid, modified amino acid, or amino acid analogue other than the following twenty genetically encoded alpha- amino acids: alanine, arginine, asparagine, aspartic acid, cysteine, glutamine, glutamic acid, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, valine. In some embodiments, unnatural amino acids may include naturally occurring compounds other than the twenty alpha-amino acids above.

Unnatural amino acids and methods of incorporating unnatural amino acids into protein sequences are known in the art, for example, as described in U.S. Patent No. 7,045,337, the contents of which are incorporated herein by reference.

IV. Methods of Using a Modified Recombinant Enzyme

In some embodiments, the disclosure provides modified recombinant enzymes and compositions which may be used for conducting in vitro polymerization reactions. In some embodiments, modified recombinant DNA polymerases provided by the disclosure may be used for in vitro reactions related to the manipulation of DNA (e.g., DNA sequencing).

Among other aspects, the disclosure provides modified recombinant enzymes (e.g., polymerases) that may be used to conduct in vitro polymerization reactions. In some

embodiments, polymerases described herein comprise one or more modifications which— individually or in combination— are useful to conduct a sequencing reaction. In some embodiments, one or more of the modifications described herein can be utilized to produce a polymerase having one or more properties useful for conducting sequencing reactions, e.g., properties such as polymerase processivity, fidelity (e.g., accuracy), substrate (e.g., nucleoside polyphosphate) binding affinity, substrate utilization (e.g., the rate at which nucleoside polyphosphates are incorporated into a growing strand complementary to a template strand), polymerase interactions with modified substrates (e.g., labeled nucleoside polyphosphates), or some combination thereof. In some embodiments, one or more of the modifications minimize or eliminate proofreading capability of the polymerase. For example, in some embodiments, one or more modifications may be made to an exonuclease domain of a polymerase that effects a loss in exonuclease activity of the polymerase.

In some aspects, the application relates to modified polymerases having altered biochemical properties that are advantageous for single molecule nucleic acid sequencing technologies. In some embodiments, variant polymerases described herein have been modified to provide improved signal readout in single molecule sequencing reactions. FIG. 1 provides an example illustration of the progression of a sequencing reaction in relation to the real-time signal readout. Without wishing to be bound by theory, it is thought that some single molecule nucleic acid sequencing reactions proceed in accordance with scheme 100. At the start of a reaction (panel I), a polymerase (dashed line) is confined in an observation region and is bound to a template strand and a primer strand. As shown, different types of nucleotides (e.g., A, G, T, C, U), each having different types of detectable labels, are present in the same reaction mixture. When the polymerase associates with a luminescently labeled nucleotide (panel II), the label becomes confined in the observation region for a period of time. During an incorporation event, for example, this period of time can be sufficient for the label to receive and/or emit energy in an amount sufficient to detect and identify its presence in the observation region. As illustrated by panels I and II of scheme 100 in relation to signal readout 102, an incorporation event can be associated with a signal pulse for a period of time corresponding to pulse width, pw.

It should be appreciated that, in some embodiments, an individual signal pulse associated with an incorporation event can be affected by a variety of conditions, such as the type of nucleotide being incorporated or the activity of the polymerase at a specific point in time. In some embodiments, an individual signal pulse can have an individual pulse width of between about 10 milliseconds and about 10 seconds. Accordingly, in some embodiments, individual pulse widths may be averaged to provide a parameter for comparative purposes. As used herein, in some embodiments,“pulse width” refers to a value corresponding to an average of a plurality of individual signal pulses, each individual signal pulse having an individual pulse width.

In some embodiments, modified polymerizing enzymes of the present application produce pulse widths of between about 10 milliseconds and about 10 seconds. In some embodiments, pulse width is at least 10 milliseconds and up to 10 seconds, at least 10

milliseconds and up to 5 seconds, at least 10 milliseconds and up to 1 second, or between about 10 milliseconds and about 1 second. In some embodiments, pulse width is between about 10 and about 500 milliseconds, between about 10 and about 200 milliseconds, between about 10 and about 100 milliseconds, between about 10 and about 50 milliseconds, between about 50 milliseconds and about 1 second, between about 50 and about 500 milliseconds, between about 50 and about 200 milliseconds, between about 50 and about 100 milliseconds, between about 100 milliseconds and about 1 second, between about 100 and about 500 milliseconds, between about 100 and about 200 milliseconds, between about 200 milliseconds and about 1 second, between about 200 and about 500 milliseconds, or between about 500 milliseconds and about 1 second.

Following incorporation of the nucleotide into the growing strand and cleavage of the luminescent label, the label diffuses out of the illumination volume and is no longer detectable in the observation region (panel III). Also as illustrated in panel III, following an incorporation event, the polymerase progresses along the template strand such that it is capable of associating with a subsequent luminescently labeled nucleotide. Similar to the progression from panel I to panel II, the signal corresponding to the progression from panel III to panel IV in signal trace 102 increases in intensity from a relatively low intensity level to a signal pulse indicative of an association event. In terms of signal trace 102, the period of time between an incorporation event and a subsequent association event can be associated with an interpulse distance, ipd.

As detailed in the foregoing with respect to pulse width, in some embodiments, an individual interpulse distance associated with a period of time between a first and second signal pulse can be affected by a variety of conditions, such as the activity or processivity of the polymerase at a specific point in time. In some embodiments, an individual interpulse distance corresponds to a period of between about 10 milliseconds and about 1 minute or longer (e.g., between about 1 and about 60 seconds, between about 1 and about 30 seconds, between about 1 and about 20 seconds, between about 1 and about 10 seconds, or less than about 1 second).

Accordingly, in some embodiments, individual interpulse distances may be averaged to provide a parameter for comparative purposes. As used herein, in some embodiments,“interpulse distance” refers to a value corresponding to an average of a plurality of individual interpulse distances.

In some embodiments, modified polymerizing enzymes of the present application produce interpulse distances of between about 10 milliseconds and about 10 seconds. In some embodiments, interpulse distance is at least 10 milliseconds and up to 10 seconds, at least 10 milliseconds and up to 5 seconds, at least 10 milliseconds and up to 1 second, or between about 10 milliseconds and about 1 second. In some embodiments, interpulse distance is between about 10 and about 500 milliseconds, between about 10 and about 200 milliseconds, between about 10 and about 100 milliseconds, between about 10 and about 50 milliseconds, between about 50 milliseconds and about 1 second, between about 50 and about 500 milliseconds, between about 50 and about 200 milliseconds, between about 50 and about 100 milliseconds, between about 100 milliseconds and about 1 second, between about 100 and about 500 milliseconds, between about 100 and about 200 milliseconds, between about 200 milliseconds and about 1 second, between about 200 and about 500 milliseconds, or between about 500 milliseconds and about 1 second.

Characteristics of a pulse width and/or an interpulse distance, in some embodiments, can be used to identify a specific luminescent label. In some embodiments, modified polymerases of the disclosure can be used in a sequencing reaction by observing a series of pulse widths indicative of the association of luminescently labeled nucleotides to determine a nucleotide sequence of a template strand. In some embodiments, artefacts in this process can give rise to incorrect sequencing information. For example, panel V illustrates a bind-and-release event in which a luminescently labeled nucleotide is confined in the observation region for a period of time sufficient to give rise to a signal pulse, but without an incorporation event.

As shown in panel V, following the detected incorporation in panel IV, the cleaved luminescent label diffuses out of the observable region ( i ). A further luminescently labeled nucleotide associates with the polymerase in the observable region to give rise to a detectable signal (ii). Rather than being incorporated into the growing strand, the luminescently labeled nucleotide dissociates from the polymerase and diffuses back into the reaction mixture (iii). As such, following a subsequently successful incorporation of the same type of nucleotide (not shown), the signal pulse corresponding to panel V would result in an apparent insertion in sequencing information readout. Accordingly, in some embodiments, modified recombinant enzymes of the present application have pulse widths of sufficient length to discern true incorporation events from these and other such artefact events. In some embodiments, modified recombinant enzymes of the present application have one or more modifications that decrease the probability of premature substrate release from a polymerase active site. In some embodiments, modified recombinant enzymes of the present application have one or more modifications that increase the probability of substrate incorporation once a substrate is associated with a polymerase active site.

In some embodiments, aspects of the present application can be used in methods related to assays of biological samples. In exemplary embodiments, methods provided herein are useful in techniques used to determine the sequence of one or more nucleic acids or polypeptides in the sample and/or to determine the presence or absence of one or more nucleic acid or polypeptide variants (e.g., one or more mutations in a gene of interest) in the sample. In some embodiments, tests can be performed on patient samples (e.g., human patient samples) to provide nucleic acid sequence information or to determine the presence or absence of one or more nucleic acids of interest for diagnostic, prognostic, and/or therapeutic purposes. In some examples, diagnostic tests can include sequencing a nucleic acid molecule in a biological sample of a subject, for example by sequencing cell free DNA molecules and/or expression products (e.g., RNA) in a biological sample of the subject. For example, the present disclosure provides methods and compositions that may be advantageously utilized in the technologies described in co-pending U.S. Patent App. Nos.: 14/543,865, 14/543,867, 14/543,888, 14/821,656, 14/821,686,

14/821,688, 15/161,067, 15/161,088, 15/161,125, 15/255,245, 15/255,303, 15/255,624,

15/261,697, 15/261,724, 62/289,019, 62/296,546, 62/310,398, 62/339,790, 62/343,997,

62/344,123, and 62/426,144, the contents of each of which are incorporated herein by reference. Some aspects of the application are useful in techniques capable of sequencing biological polymers, such as nucleic acids and proteins. In some embodiments, methods and compositions described in the application can be used in techniques that identify a series of nucleotide or amino acid monomers that are incorporated into a nucleic acid or protein (e.g., by detecting a time-course of incorporation of a series of labeled nucleotide or amino acid monomers). In some embodiments, methods and compositions described in the application can be incorporated into techniques that identify a series of nucleotides that are incorporated into a template-dependent nucleic acid sequencing reaction product synthesized by a polymerizing enzyme.

During sequencing, a polymerizing enzyme may couple (e.g., attach) to a priming location of a target nucleic acid molecule (e.g., a nucleic acid molecule of a sequencing template). The priming location can comprise a primer that is complementary to a portion of the target nucleic acid molecule. As an alternative the priming location is a gap or nick that is provided within a double stranded segment of the target nucleic acid molecule. A gap or nick can be from 0 to at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, or 40 nucleotides in length. A nick can provide a break in one strand of a double stranded sequence, which can provide a priming location for a polymerizing enzyme, such as, for example, a strand displacing polymerase enzyme.

In some cases, a sequencing primer can be annealed to a target nucleic acid molecule that may or may not be immobilized to a solid support. A solid support can comprise, for example, a sample well on an integrated device used for nucleic acid sequencing. In some embodiments, a sequencing primer may be immobilized to a solid support and hybridization of the target nucleic acid molecule also immobilizes the target nucleic acid molecule to the solid support. In some embodiments, a polymerase is immobilized to a solid support and soluble primer and target nucleic acid are contacted to the polymerase. However, in some embodiments a complex comprising a polymerase, a target nucleic acid and a primer is formed in solution and the complex is immobilized to a solid support (e.g., via immobilization of the polymerase, primer, and/or target nucleic acid). In some embodiments, none of the components in a sample well are immobilized to a solid support. For example, in some embodiments, a complex comprising a polymerase, a target nucleic acid, and a primer is formed in solution and the complex is not immobilized to a solid support. In some embodiments, a modified recombinant enzyme is immobilized on a surface. In some embodiments, the surface comprises a nanoaperture. In certain embodiments, the nanoaperture comprises a bottom surface comprising a first material and sidewalls formed by a plurality of metal or metal oxide layers. In some embodiments, the first material is a transparent material or glass. In some embodiments, the bottom surface is flat. In some embodiments, the bottom surface is a curved well. In some embodiments, the bottom surface includes a portion of the sidewalls below the sidewalls formed by a plurality of metal or metal oxide layers. In some embodiments, the first material is fused silica or silicon dioxide. In some embodiments, the plurality of layers each comprise a metal (e.g., Al, Ti) or metal oxide (e.g., A1203, Ti02, TiN). In some embodiments, the surface can be a surface of a chip made from glass or other transparent material, silica, fused silica, silicon dioxide, a polymer, other material, or a combination thereof (e.g., a combination of different layers, for example including one or more metal layers).

Under appropriate conditions, a polymerase enzyme that is contacted to an annealed primer/target nucleic acid can add or incorporate one or more nucleotides onto the primer, and nucleotides can be added to the primer in a 5' to 3', template-dependent fashion. Such incorporation of nucleotides onto a primer (e.g., via the action of a polymerase) can generally be referred to as a primer extension reaction. Each nucleotide can be associated with a detectable tag that can be detected and identified (e.g., based on its luminescent lifetime and/or other characteristics) during the nucleic acid extension reaction and used to determine each nucleotide incorporated into the extended primer and, thus, a sequence of the newly synthesized nucleic acid molecule. Via sequence complementarity of the newly synthesized nucleic acid molecule, the sequence of the target nucleic acid molecule can also be determined. In some cases, annealing of a sequencing primer to a target nucleic acid molecule and incorporation of nucleotides to the sequencing primer can occur at similar reaction conditions (e.g., the same or similar reaction temperature) or at differing reaction conditions (e.g., different reaction temperatures). In some embodiments, sequencing by synthesis methods can include the presence of a population of target nucleic acid molecules (e.g., copies of a target nucleic acid) and/or a step of amplification of the target nucleic acid to achieve a population of target nucleic acids. However, in some embodiments, sequencing by synthesis is used to determine the sequence of a single molecule in each reaction that is being evaluated (and nucleic acid amplification is not required to prepare the target template for sequencing). In some embodiments, a plurality of single molecule sequencing reactions are performed in parallel (e.g., on a single integrated device) according to aspects of the present application. For example, in some embodiments, a plurality of single molecule sequencing reactions are each performed in separate reaction chambers on an integrated device.

In some embodiments, polymerizing enzymes of the disclosure are useful in single molecule sequencing reactions conducted in sample wells of considerably small volumes. For example, the volume of a sample well may be between about 10 ²¹ liters and about 10 ¹⁵ liters, in some implementations. Because the sample well has a small volume, detection of single-sample events (e.g., single-molecule events) are achievable. In some embodiments, a surface (e.g., a surface of a sample well) is configured to receive a polymerase described herein. In some embodiments, a sample well receives a polymerase that may be disposed on a surface of the sample well, such as a bottom surface. In some embodiments, a sample well is formed within an integrated device, wherein the bottom surface of the sample well is distal to the surface of the integrated device into which it is formed.

In certain embodiments, techniques described herein relate to polymerizing enzymes, and complexes thereof, which may be added to a sample well. In some embodiments, polymerizing enzymes described herein may be confined in a target volume of the sample well (e.g., a reaction volume). In some embodiments, the target volume is a region within a sample well. In embodiments when one or more polymerizing enzymes are to be immobilized on the bottom surface, it may be desirable to functionalize the bottom surface to allow for attachment of the one or more polymerizing enzymes (e.g., polymerizing enzymes and complexes thereof). In some embodiments, the bottom surface is functionalized with a material comprising a coupling group. For example, the coupling group may comprise chemical moieties, such as amine groups, carboxyl groups, hydroxyl groups, sulfhydryl groups, metals, chelators, and the like.

Alternatively, they may include specific binding elements, such as biotin, bis-biotin, avidin, streptavidin, neutravidin, lectins, SNAP-tags™ or substrates therefore, associative or binding peptides or proteins, antibodies or antibody fragments, nucleic acids or nucleic acid analogs, or the like. Additionally, or alternatively, the coupling group may be used to couple an additional group that is used to couple or bind with a molecule of interest (e.g., a polymerizing enzyme or complex thereof), which may, in some cases include both chemical functional groups and specific binding elements. By way of example, a coupling group, e.g., biotin or bis-biotin, may be deposited upon a substrate surface and selectively activated in a given area. An intermediate binding agent, e.g., streptavidin, may then be coupled to the first coupling group. The molecule of interest (e.g., a polymerizing enzyme or complex thereof), which in this particular example would be biotinylated, is then coupled to the streptavidin. In some embodiments, polymerizing enzymes described herein may further compri ses a coupling moiety capable of forming an interaction with a coupling group that immobilizes the polymerase to a surface (e.g., a surface of a sample well). For example, in some embodiments, polymerizing enzymes comprise N-terminal or C-terminal biotinylation or bis-biotinylation sequences capable of binding to an avidin protein. In some embodiments, a biotinylation or bis-biotinylation sequence further comprises a linker sequence. For example, in some embodiments, a C-terminal linker/biotinylation sequence comprises the amino acid sequence GGGS GGGS GGGS GLNDFFE AQKIEWHE (SEQ ID NO: 843). In some embodiments, polymerizing enzymes comprise N-terminal or C -terminal bis- biotinylation sequences capable of binding to two binding sites of an avidin protein. For example, in some embodiments, an N-terminal or C-terminal linker/bis-biotinylation sequence comprises the amino acid sequence

GGGGS GGGS GGGS GLNDFFE AQKIEWHEGGGS GGGS GGGS GLNDFFE AQKIEWHE

(SEQ ID NO: 844).

EXAMPLES

Example 1. Expression and Evaluation of Modified Polymerases

Recombinant polymerase variants were expressed in E. coli and purified from 150 mL scale cultures using His-spin columns. Protein purity was analyzed by SDS-PAGE followed by Coomassie Blue staining (FIG. 7). Following buffer exchange and protein concentration, the recombinant variants were evaluated for activity and processivity in the presence of dNTPs with trap chase for 30 minutes at 30 °C. Chimeric polymerase variants C017 and C020 showed activity, processivity, and length of synthesis in the presence of a trap. Utilization of dNTP analogs by variant polymerases was measured to evaluate suitability of the polymerases in sequencing reactions. Both homologous mutant variants and chimeric polymerase variants displayed utilization of dN6Ps. Results from single molecule sequencing are shown below in TABLE 8.

Table 8. Sequencing Results with Modified Polymerases

Example 2. Modified Polymerases with Improved Substrate Utilization

The E. faecium polymerase variant, EFM37, contains three active site substitutions at positions L264, V261, and K500 that were determined to improve utilization of hexaphosphate substrates (dN6Ps). Dumbbell ternary complexes with EFM37, or related variants such as

EFM48, were observed to load on sequencing chips and to undergo processive DNA replication both inside sample wells and on the top surface using unlabeled dN6Ps (10 mM) based on nanoball assays (FIGs. 8A-8D). DNA nanoballs were generated by loading sequencing chips with EFM37-dumbbell ternary complexes and 1-hour replication with 10 pM dN6Ps followed by incubation with FAM-labeled oligonucleotide probe.

In subsequent experiments using dye-labeled dN6P substrates containing a duplex DNA linker between dN6P and dye, real-time DNA synthesis was not observed. A real-time stopped- flow assay for short fork strand displacement DNA synthesis was used to further evaluate variants EFM37, EFM48 and EMF66. The real-time stopped-flow strand-displacement DNA synthesis assay utilized a short fork DNA substrate in which primer extension, upon rapid addition of nucleotides and Mg ⁺⁺ (10 mM MgCh) at 30 °C, results in strand displacement and unquenching of a FAM-labeled displaced oligonucleotide (FIG. 10A). Based on the assay results, it was determined that DNA synthesis rates were approximately 3-10 times slower in rate (base pairs per second) with the duplex DNA linker analogs compared to the dN6Ps (FIGs. SC- 8D). It was determined that E. faecium has an overall negatively charged surface, including in the vicinity of the polymerase active site, and a relatively low theoretical isoelectric point (pi = 5.5). Based on this understanding and other observations, it was hypothesized that electrostatic repulsion between the negatively charged nucleotide analog and the E. faecium polymerase surface contributed to the poor utilization of these analogs.

The wild-type E. faecium structure was computationally modeled, and surface positions in the vicinity of the active site were identified for introduction of substitutions to make this region more electropositive, and therefore more attractive to negatively charged analogs, including DNA-linker analogs, while minimally affecting structural stability. A depiction of the modeled structure is shown in FIG. 9A, with negatively charged residues shown colored, and the location of catalytic aspartate residues in the polymerase active site indicated by an arrow. The polymerase homology domains map to regions of the E. faecium polypeptide as shown in FIG. 9B, which is oriented in an N-terminal to C-terminal fashion with start position of each domain indicated. A total of 12 substitutions affecting surface charge were designed, including nine negative-to-positive substitutions, and multiple combinations of these were screened for dN6P and DNA linker analog utilization in two rounds of screening.

All E. faecium variants screened contained the same three active site mutations as the parent enzyme EFM37 (L264H, V261A, K500E), and EFM37 was purified and screened by stopped-flow strand-displacement synthesis assays in parallel as a reference from which to identify improvements in rate. After two rounds of screening, two related variants— EFM88 and EFM89— were identified with major increases in incorporation rate with both dN6Ps (2.0-2.7- fold) and DNA-linker analogs (6.3-8.7-fold) relative to EFM37 (FIG. 10A). EFM88 and EFM89 both contain nine surface charge substitutions, seven of which are in common, and a total of 13 substitutions relative to wild-type. These changes result in the net elimination of seven negative charges and addition of five positive charges (FIG. 10B) in the region surrounding the entrance to the polymerase active site, resulting in a major remodeling of the electrostatic surface in this area. A comparison between the modeled wild-type and EFM88 electrostatic surfaces is shown in FIG. IOC.

The EFM88 and EFM89 variants were evaluated in single-molecule sequencing reactions using DNA linker analog substrates. Ternary complexes containing EFM88 or EFM89 were generated with primed M13 plasmid DNA and loaded onto sequencing chips. Upon initiation of sequencing reactions with buffer containing dye-labeled DNA-linker analogs, pulsing characteristic of nucleotide incorporation was observed, and sequencing alignments to the M13 reference sequence were obtained in the range of 67-82% accuracy using data collected with an avalanche photodiode instrument. Results are shown in FIGs. 10D-10F. An example alignment with EFM89 is also shown in FIG. 11.

To further evaluate these findings, ternary complexes (2 kb template DNA derived by PCR from lambda phage) made with EFM89 from two independent expression and purification batches were evaluated in further sequencing reactions using a commercial platform. Both batches of EFM89 displayed consistent sequencing results (FIGs. 12A-12D), with 74-76% accuracy and an approximate 3 kb read length.

Example 3. Modified recombinant enzymes with Improved Stability

Due to the destabilizing effect of a high level of substitutions (13 total), EFM88 and EFM89 display lower purification yield and active fraction than wild-type E. faecium

polymerase, and low loading and short read length in single-molecule sequencing.

Using rational design principles and computational tools, three panels of EFM89-based variants were designed containing substitutions to improve stability: 1. reversions or substitutions in the polymerase active site (EFM144-154); 2. novel stability substitutions in the exonuclease domain or TPR1 sub-domain (EFM155-160); and 3. reversions at six residues located on the polymerase surface (EFM161-166). With these panels, an automated small-scale purification workflow for EFMs optimized for on-chip screening was used. Miniaturization of the EFM process involved modification and optimization of a number of steps, including use of tube cultures, in-lysate streptavidin complexing, and one-step purification with low stringency buffers compatible with EFMs. This method produced high yield for wild-type E. faecium polymerase and sufficient yield for on-chip screening for a number of candidates (FIG. 16).

EFM158, containing the single substitution E60L (relative to EFM158), displayed remarkably higher yield in this method (FIG. 16). This increase in yield indicates that introduction of E60L results in a major improvement in protein stability.

E. faecium polymerase contains a glutamate at position 60, whereas all other homologs contain leucine (see the multiple sequence alignment in FIG. 17. The strong sequence

conservation of leucine at this position is observed even among very distant homologs (<30% identity). This conserved leucine residue is buried in the hydrophobic core of the exonuclease domain. The hydrophobic environment surrounding E60 in an in-house E. faecium polymerase crystal structure and L60 in chimera C320 is displayed in FIG. 18.

Multiple EFM variants were tested on a commercial platform using 2kb templates. Here, in agreement with its dramatic increase in yield, EFM 158 displayed major improvements in loading, read length, N50, and percent of wells still active at the end of the 6-hour sequencing run (FIG. 19). Compared to EFM89, read length increased 80% from 3kb to 5.4kb. Due to an improved read length distribution (FIG. 20) the N50 read length increased from 4kb to 8.6kb with EFM158 (meaning 50% of the data is in reads longer 8.6kb). The increased read length of EFM158 may be due to increased stability/survivability of the enzyme and/or ternary complex under sequencing conditions, as indicated by a major increase in the percentage of wells that are still actively replicating at the end of the 6-hour run from 0.9% to 12.2%. A comparison of the surface charges of the EFM158 and wild-type E. faecium polymerase is provided in FIG. 21.

Example 4. Additional Polymerases Variants

EFM158 provides a much more solid backbone for evolving new EFM candidates with improved sequencing performance. The increased yield and on-chip loading enable improved screening methodology, including automated high-throughput purification and multiplexed single-molecule sequencing.

As such, EFM 158 was used as a backbone to screen for additional EFM variants of interest. A number of these EFM variants demonstrated increased accuracy and/or have other effects on sequencing such as interpulse duration (FIG. 22), pulse width, and read length (FIG. 23).

Example 5. Substitutions enriched in emulsion-based IVTT-RCA screen with EF polymerase

A gene encoding EF polymerase was subjected to random mutagenesis using mutagenic PCR and sub-cloned into a circular construct suitable for protein expression in an in-vitro transcription and translation (IVTT) expression system followed by rolling-circle replication (IVTT-RCA). The mutagenized EF polymerase library was annealed with a primer for DNA- replication and emulsified into femtoliter-scale droplets using a microfluidic chip (Leman et al. Lab Chip, 2015,15, 753-765) in a buffer containing IVTT components, dNTPs, and Mg++; emulsification of the library resulted in a single gene per droplet. The emulsion was incubated at 30 degrees for 16 hours. In this manner, the droplet-isolated EF variants were allowed to replicate their own genes by RCA, resulting in enrichment of DNA sequences encoding EF variants containing favorable substitutions that increase their replication capacity; substitutions responsible for increased replication capacity can include improved protein stability and yield, processivity, strand-displacement, DNA-binding, and speed. After IVTT-RCA, the emulsion was broken and replicated DNA was recovered and subjected to PCR with primers designed to recover amplicons containing the full-length genes from the RCA products. The amplicons were subjected to an additional round of IVTT-RCA selection or ligated with hairpin adapters and subjected to high-throughput single-molecule DNA sequencing in order to identify the substitutions present in the recovered genes. The starting library (i.e., before IVTT-RCA selection) was also sequenced to serve as a reference. Enriched substitutions after 2 rounds of IVTT-RCA selection were identified by comparing the relative abundance (fraction of reads containing the substitution) of each substitution in the set of pre- and post-selection sequence reads (FIG. 25).

EMBODIMENTS

In some embodiments, the present disclosure provides:

1. A recombinant polymerizing enzyme based on a first polymerizing enzyme selected from Table 1, wherein at least one amino acid segment of the first polymerizing enzyme has been replaced with a corresponding amino acid segment from a second polymerizing enzyme selected from Table 1, wherein the first and second polymerizing enzymes are different, and optionally wherein the recombinant polymerizing enzyme further comprises one or more amino acid insertions, deletions, or substitutions relative to a sequence of the first and/or second polymerizing enzyme of Table 1. In particular embodiments, the first polymerizing enzyme is E. faecium polymerase (SEQ ID Nos: 2-5). In particular embodiments, the first polymerizing enzyme is selected from any one of SEQ ID Nos. 23-33.

2. The recombinant polymerizing enzyme of paragraph 1, wherein the first polymerizing enzyme is F29 polymerase (SEQ ID NO: 1) and the second polymerizing enzyme is selected from any one of SEQ ID NOs: 2-33. In particular embodiments, the second polymerizing enzyme is selected from SEQ ID Nos: 2-5. In particular embodiments, the second polymerizing enzyme is selected from SEQ ID Nos: 23-33.

3. The recombinant polymerizing enzyme of any prior paragraph, wherein at least one to three additional amino acid segments of the first polymerizing enzyme have been replaced with corresponding amino acid segments from one or more polymerizing enzymes of Table 1, wherein the one or more polymerizing enzymes of Table 1 are different from the first

polymerizing enzyme, and optionally wherein one or more of the corresponding amino acid segments comprises one or more amino acid insertions, deletions, or substitutions relative to their sequence in Table 1.

4. The recombinant polymerizing enzyme of any prior paragraph, wherein one or more of the segments comprises a domain of a polymerizing enzyme of Table 1.

5. The recombinant polymerizing enzyme of any prior paragraph, wherein one or more of the amino acid segments comprises a portion of a domain of a polymerizing enzyme of Table 1. 6. The recombinant polymerizing enzyme of paragraph 4 or 5, wherein one or more of the amino acid segments comprise one or more amino acids flanking the domain or portion thereof in a polymerizing enzyme of Table 1.

7. The recombinant polymerizing enzyme of any prior paragraph, wherein at least one amino acid insertion, deletion, or substitution corresponds to an amino acid insertion, deletion, or substitution found in a different naturally-occurring polymerizing enzyme of Table 1.

8. The recombinant polymerizing enzyme of any prior paragraph, wherein at least one amino acid insertion, deletion, or substitution corresponds to an amino acid insertion, deletion, or substitution that is not found in a naturally-occurring polymerizing enzyme of Table 1.

9. The recombinant polymerizing enzyme of any prior paragraph, wherein the one or more corresponding amino acid segments are selected from the group consisting of: amino acids 1-51 from the M2Y polymerase, amino acids 271-375 from the E. faecium polymerase, amino acids 72-89 from the E. faecium polymerase, and/or amino acids 445-449 from the E. faecium polymerase.

10. The recombinant polymerizing enzyme of any prior paragraph, wherein at least one amino acid insertion, deletion, or substitution is at a position corresponding to a position selected from positions: M8, V51, N62, 171, L107, K131, K135, L142, G135, L142, Y148,

G197, Y224, Y226, E239, V250, N251, L253, Y281, 1288, T301, R306, R308, D325, D341, K354, T368, E375, K379, Q380, A437, A444, P447, E466, D476, K478, A484, E508, D510, K512, E515, K539, D570, and T571 in F29 polymerase.

11. The recombinant polymerizing enzyme of paragraph 10, comprising one or more amino acid substitutions selected from M8R, V51A, N62D, 17 IV, L107I, K131E, K135Q, L142K, Y148I, G197D, Y224K, Y226F, E239G, V250A, V250I, N251R, L253A, L253H, Y281H, I288L, T301C, R306Q, R308L, D325E, D341E, K354R, T368F, E375K, E375Y, K379R, Q380R, A437G, A444T, E466K, D476H, P477D, K478D, A484C, A484Q, A484N, A484E, A484D, A484K, A484R, A484H, A484Y, and A484X (where X represents an unnatural amino acid, as described herein), E508R, D510K, D510R, K512Y, E515Q, K539E, D570S, and T571V.

12. The recombinant polymerizing enzyme of any prior paragraph, comprising one or more amino acid substitutions at positions corresponding to 171, L107, K135, L142, G197,

Y224, E239, V250, L253, E375, A437, A444, E466, D476, A484, E508, D510, K512, E515, K539, D570, and T571 in SEQ ID NO: 1. 13. The recombinant polymerizing enzyme of paragraph 12, wherein the one or more amino acid substitutions are selected from 17 IV, L107I, K135Q, L142K, G197V, Y224K, E239G, V250I, L253A, E375Y, A437G, A444V, E466K, D476H, A484E, E508R, D510R, K512Y, E515Q, K539E, D570S, and T571V in SEQ ID NO: 1.

14. The recombinant polymerizing enzyme of any prior paragraph, comprising one or more amino acid substitutions at positions corresponding to K131, K135, L142, Y148, Y224, E239, V250, L253, R306, R308, E375, A437, E466, D476, A484, E508, D510, K512, E515, K539, D570, and T571 in SEQ ID NO: 1.

15. The recombinant polymerizing enzyme of paragraph 14, wherein the one or more amino acid substitutions are selected from K131E, K135Q, L142K, Y148I, Y224K, E239G, V250A, V250I, L253A, L253H, R306Q, R308L, E375Y, A437G, E466K, D476H, A484E, E508R, D510K, D510R, K512Y, E515Q, K539E, D570E, D570S, and T571V in SEQ ID NO: 1.

16. The recombinant polymerizing enzyme of paragraph 14, wherein the one or more amino acid substitutions are selected from K131E, L142K, Y148I, Y224K, E239G, V250A, L253H, E375Y, A437G, A484E, E508R, D510K, K512Y, E515Q, and D570E in SEQ ID NO: 1.

17. The recombinant polymerizing enzyme of any prior paragraph, wherein at least one or more of the substituted segments comprises an exonuclease region, a palm region, a TPR1 region, a fingers region, a TPR2 region, a thumb region, or a portion of any one thereof, and optionally comprising one or more flanking amino acids.

18. A recombinant polymerizing enzyme having an amino acid sequence that is at least 60%, 60-70%, 70-80%, or at least 80% identical to an amino acid sequence of Table 1 and comprising one or more amino acid modifications of Tables 2-7. In particular embodiments, the amino acid sequence of Table 1 is selected from any one of SEQ ID Nos. 2-5. In particular embodiments, the amino acid sequence of Table 1 is selected from any one of SEQ ID Nos. 23- 33.

19. The recombinant polymerizing enzyme of paragraph 18, wherein the one or more amino acid modifications include at least one amino acid mutation.

20. The recombinant polymerizing enzyme of paragraph 18, wherein the one or more amino acid modifications include at least one domain substitution.

21. The recombinant polymerizing enzyme of paragraph 18, wherein the one or more amino acid modifications include at least one domain substitution and at least one amino acid mutation. 22. The recombinant polymerizing enzyme of paragraph 18 having a sequence selected from Table 2 or the recombinant polymerizing enzyme of paragraph 18 having a combination of modifications listed in Table 7.

23. The recombinant polymerizing enzyme of paragraph 18 having a sequence selected from Table 3 or Table 4.

24. The recombinant polymerizing enzyme of any prior paragraph, further comprising a purification tag.

25. The recombinant polymerizing enzyme of paragraph 24, wherein the purification tag is a C-terminal tag.

26. The recombinant polymerizing enzyme of paragraph 24, wherein the purification tag is an N-terminal tag.

27. The recombinant polymerizing enzyme of paragraph 24, 25, or 26, wherein the purification tag is a His tag.

28. The recombinant polymerizing enzyme of any prior paragraph, further comprising a coupling group.

29. The recombinant polymerizing enzyme of paragraph 28, wherein the coupling group is attached at a C-terminal end of the recombinant polymerizing enzyme.

30. The recombinant polymerizing enzyme of paragraph 28, wherein the coupling group is attached at an N-terminal end of the recombinant polymerizing enzyme.

31. The recombinant polymerizing enzyme of paragraph 28, 29, or 30, wherein the coupling group is a biotinylation sequence or a bis-biotinylation sequence.

32. The recombinant polymerizing enzyme of any prior paragraph comprising a His tag and a biotinylation sequence or a bis-biotinylation sequence.

33. The recombinant polymerizing enzyme of paragraph 18 immobilized on a surface.

34. The recombinant polymerizing enzyme of paragraph 33, wherein the surface comprises a nanoaperture.

35. An isolated nucleic acid molecule that encodes the recombinant polymerizing enzyme of paragraph 18.

36. A composition comprising the recombinant polymerizing enzyme of paragraph

18.

37. A method of sequencing a nucleic acid, the method comprising contacting the recombinant polymerizing enzyme of paragraph 18 with a sequencing reaction mixture.

38. A recombinant polymerizing enzyme having an amino acid sequence that is at least 60%, 60-70%, 70-80%, or at least 80% identical to an amino acid sequence of Table 1 and comprising an exonuclease region that is at least 60%, 60-70%, 70-80%, or at least 80% identical to an exonuclease region from a different polymerizing enzyme of Table 1, Table 2, Table 3, or Table 4. In particular embodiments, the amino acid sequence of Table 1 is selected from any one of SEQ ID Nos. 2-5. In particular embodiments, the amino acid sequence of Table 1 is selected from any one of SEQ ID Nos. 23-33.

39. A recombinant polymerizing enzyme having an amino acid sequence that is at least 60%, 60-70%, 70-80%, or at least 80% identical to an amino acid sequence of Table 1 and comprising a palm region that is at least 60%, 60-70%, 70-80%, or at least 80% identical to a palm region from a different polymerizing enzyme of Table 1, Table 2, or Table 3. In particular embodiments, the amino acid sequence of Table 1 is selected from any one of SEQ ID Nos. 2-5. In particular embodiments, the amino acid sequence of Table 1 is selected from any one of SEQ ID Nos. 23-33.

40. A recombinant polymerizing enzyme having an amino acid sequence that is at least 60%, 60-70%, 70-80%, or at least 80% identical to an amino acid sequence of Table 1 and comprising a TPR1 region that is at least 60%, 60-70%, 70-80%, or at least 80% identical to a TPR1 region from a different polymerizing enzyme of Table 1, Table 2, or Table 3. In particular embodiments, the amino acid sequence of Table 1 is selected from any one of SEQ ID Nos. 2-5. In particular embodiments, the amino acid sequence of Table 1 is selected from any one of SEQ ID Nos. 23-33.

41. A recombinant polymerizing enzyme having an amino acid sequence that is at least 60%, 60-70%, 70-80%, or at least 80% identical to an amino acid sequence of Table 1 and comprising a fingers region that is at least 60%, 60-70%, 70-80%, or at least 80% identical to a fingers region from a different polymerizing enzyme of Table 1, Table 2, or Table 3. In particular embodiments, the amino acid sequence of Table 1 is selected from any one of SEQ ID Nos. 2-5. In particular embodiments, the amino acid sequence of Table 1 is selected from any one of SEQ ID Nos. 23-33.

42. A recombinant polymerizing enzyme having an amino acid sequence that is at least 80% identical to an amino acid sequence of Table 1 and comprising a TPR2 region that is at least 80% identical to a TPR2 region from a different polymerizing enzyme of Table 1, Table 2, or Table 3. In particular embodiments, the amino acid sequence of Table 1 is selected from any one of SEQ ID Nos. 2-5. In particular embodiments, the amino acid sequence of Table 1 is selected from any one of SEQ ID Nos. 23-33.

43. A recombinant polymerizing enzyme having an amino acid sequence that is at least 60%, 60-70%, 70-80%, or at least 80% identical to an amino acid sequence of Table 1 and comprising a thumb region that is at least 60%, 60-70%, 70-80%, or at least 80% identical to a thumb region from a different polymerizing enzyme of Table 1, Table 2, or Table 3. In particular embodiments, the amino acid sequence of Table 1 is selected from any one of SEQ ID Nos. 2-5. In particular embodiments, the amino acid sequence of Table 1 is selected from any one of SEQ ID Nos. 23-33.

44. A recombinant polymerizing enzyme having an amino acid sequence that is at least 60%, 60-70%, 70-80%, or at least 80% identical to an amino acid sequence of Table 1 and comprising two or more regions of any of the prior paragraphs. In particular embodiments, the amino acid sequence of Table 1 is selected from any one of SEQ ID Nos. 2-5. In particular embodiments, the amino acid sequence of Table 1 is selected from any one of SEQ ID Nos. 23- 33.

45. A sequencing method comprising performing a sequencing reaction using one or more polymerases of any prior paragraph.

46. A modified recombinant enzyme comprising a first segment and a second segment, wherein:

the first segment comprises an amino acid sequence corresponding to a first reference segment, said first reference segment containing amino acids 197-271 of SEQ ID NO: 2, wherein the amino acid sequence of the first segment is at least 80%, 80-90%, 90-95%, or at least 95% identical to the amino acid sequence of the first reference segment, and wherein the first segment has a higher isoelectric point than the first reference segment; and

the second segment comprises an amino acid sequence corresponding to a second reference segment, said second reference segment containing amino acids 443-528 of SEQ ID NO: 2, wherein the amino acid sequence of the second segment is at least 80%, 80-90%, 90-95%, or at least 95% identical to the amino acid sequence of the second reference segment, and wherein the second segment has a higher isoelectric point than the second reference segment. In particular embodiments, the first segment comprises an amino acid sequence that is at least 80%, 80-90%, 90-95%, or at least 95% identical to 197-271 of SEQ ID NO: 2 and the second segment comprises an amino acid sequence that is at least 80%, 80-90%, 90-95%, or at least 95% identical to amino acids 443-528 of SEQ ID NO: 2.

47. A modified recombinant enzyme comprising a first segment comprising an amino acid sequence corresponding to a reference segment, said reference segment containing amino acids 1-196 of SEQ ID NO: 2, wherein the amino acid sequence of the first segment is at least 80%, 80-90%, 90-95%, or at least 95% identical to the amino acid sequence of the reference segment; and wherein the first segment has a higher isoelectric point than the reference segment. In particular embodiments, the first segment comprises an amino acid sequence that is at least 80%, 80-90%, 90-95%, or at least 95% identical to 1-196 of SEQ ID NO: 2.

48. A modified recombinant enzyme comprising a first segment and a second segment, wherein:

the first segment comprises an amino acid sequence corresponding to a first reference segment, said first reference segment containing amino acids 1-271 of SEQ ID NO: 2, wherein the amino acid sequence of the first segment is at least 80%, 80-90%, 90-95%, or at least 95% identical to the amino acid sequence of the first reference segment, and wherein the first segment has a higher isoelectric point than the first reference segment; and

the second segment comprises an amino acid sequence corresponding to a second reference segment, said second reference segment containing amino acids 443-528 of SEQ ID NO: 2, wherein the amino acid sequence of the second segment is at least 80%, 80-90%, 90-95%, or at least 95% identical to the amino acid sequence of the second reference segment, and wherein the second segment has a higher isoelectric point than the second reference segment. In particular embodiments, the first segment comprises an amino acid sequence that is at least 80%, 80-90%, 90-95%, or at least 95% identical to 1-271 of SEQ ID NO: 2 and the second segment comprises an amino acid sequence that is at least 80%, 80-90%, 90-95%, or at least 95% identical to amino acids 443-528 of SEQ ID NO: 2.

49. The modified recombinant enzyme of any one of paragraphs 46-48, wherein the amino acid sequence of the modified recombinant enzyme comprises a modification at one or more positions corresponding to K4, T13, S22, V25, C26, D27, N33, 134, F36, S42, D54, N59, E60, E65, E85, M95, N106, T110, T114, K119, Q122, Y133, P136, E139, E142, N145, P147, 1148, E152, 1153, P160, D167, D171, N175, F188, D189, Q206, T211, S216, R217, D232, A236, V247, 1253, V261, L264, S267, V443, L445, A446, S447, V449, T450, W452, G453, Y455, F465, N467, T479, E482, A484, E485, A486, L490, D492, S493, K495, K500, S503, Q506, Q513, E519, D521, E523, and V526 of SEQ ID NO: 2.

50. The modified recombinant enzyme of paragraph 49, wherein a modification is an amino acid substitution selected from the group consisting of K4R, T13N, S22A, V25L, C26W, D27E, N33T, I34V, F36V, S42T, D54Y, N59D, E60L, E60V, E65S, E85P, M95T, M95K, N106G, T110I, T114S, K119Q, Q122V, Y133L, P136T, E139K, E139Q, E139R, E139H,

E142K, E142Q, E142R, E142H, N145K, P147Q, P147T, I148K, I148H, I148R, E152D, I153V, P160A, D167P, D167K, D171K, D171H, D171R, N175T, F188C, D189K, D189H, D189R, Q206R, Q206K, Q206H, T211A, S216G, S216R, R217G, D232K, A236G, V247D, I253H, I253A, V261A, V261I, V261L, L264H, L264A, L264M, S267A, V443T, L445M, A446G, S447V, V449I, T450A, W452Y, G453A, Y455W, F465Y, N467R, N467K, N467H, N467S, N467T, T479V, E482K, E482H, E482R, A484E, E485D, A486E, L490M, D492H, D492K, D492R, D492A, H492S, S493P, K495R, K500E, S503A, S503T, Q506K, Q513D, D521K, D521R, D521H, E523R, E523V, E523Y, E523F, E523H, E523W, and V526L.

51. The modified recombinant enzyme of paragraph 49 or paragraph 50, wherein the amino acid sequence of the modified recombinant enzyme comprises a modification at one or more positions corresponding to E139, E142, N145, 1148, D167, D171, D189, N467, E482, D492, K495, D521, and E523.

52. The modified recombinant enzyme of paragraph 51, wherein a modification is an amino acid substitution selected from the group consisting of E139K, E139Q, E139R, E139H, E142K, E142H, E142R, E142Q, N145K, I148K, I148H, I148R, D167P, D167K, D171K, D171H, D171R, D189K, D189H, D189R, N467R, N467K, N467H, N467S, N467T, E482K, E482H, E482R, D492H, D492K, D492R, K495R, D521K, D521H, D521R, E523K, E523Y, E523H, E523R, E523F, and E523W.

53. The modified recombinant enzyme of any one of paragraphs 46-52, wherein the amino acid sequence of the modified recombinant enzyme comprises a modification at one or more positions corresponding to P273, P275, R308, V315, Q317, S319, L320, 1322, Q323, D337, E338, D341, T345, F352, F353, T364, D374, 1384, E385, N388, E391, A396, N397, G400, D414, D425, R429, E436, L437, D533, R534, E537, G547, E545, L555, P556, R558, T559, V564, T568, M569, and T571 of SEQ ID NO: 2.

54. The modified recombinant enzyme of paragraph 53, wherein a modification is an amino acid substitution selected from the group consisting of P273S, P275S, E283K, V315L, S319R, R308G, G308R, Q317R, S319R, L320M, L320T, I322K, Q323G, Q323V, Q323R, D337G, E338K, D341T, T345I, F352I, F353C, T364I, D374G, I384T, I384F, I384S, E385Y, E385Y, N388T, E391Y, E391W, E391F, E391H, E391M, E391K, E391R, A396Q, N397L, G400L, D414V, D425N, R429G, E436R, E436G, L437Y, L437E, D533A, R534K, E537K, E537H, E537R, E545K, G547S, L555K, L555R, P556A, R558H, T559V, V564L, T568D, T568S, M569K, M569T, M569V, and T571S.

55. The modified recombinant enzyme of paragraph 53, wherein a modification is an amino acid substitution selected from the group consisting of D374G, E385Y, E391Y, E391W, E391K, E391F, D533A, E537K, E537H, E537R, and E545K.

56. The modified recombinant enzyme of any one of paragraphs 53-55, wherein the modified recombinant enzyme comprises a combination of modifications listed in Table 7. 57. The modified recombinant enzyme of any one of paragraphs 53-55, wherein the amino acid sequence of the modified recombinant enzyme comprises a modification at positions corresponding to E142, 1148, D189, V261, L264, R308, E391, E482, D492, K500, D521, E523, and E537.

58. The modified recombinant enzyme of paragraph 57, wherein:

the modification at position E142 is E142K;

the modification at position 1148 is I148K;

the modification at position D 189 is D189K;

the modification at position V261 is V261A;

the modification at position L264 is L264H;

the modification at position R308 is R308G;

the modification at position E391 is E391Y;

the modification at position E482 is E482K;

the modification at position D492 is D492H;

the modification at position K500 is K500E;

the modification at position D521 is D521K;

the modification at position E523 is E523K; and

the modification at position E537 is E537K.

59. The modified recombinant enzyme of paragraph 58, wherein the modified recombinant enzyme comprises the amino acid sequence of SEQ ID NO: 88.

60. The modified recombinant enzyme of paragraph 58, wherein the amino acid sequence of the modified recombinant enzyme comprises a modification at position E60.

61. The modified recombinant enzyme of paragraph 60, wherein the modification at E60 is E60L.

62. The modified recombinant enzyme of paragraph 61, wherein the modified recombinant enzyme comprises the amino acid sequence of SEQ ID NO: 157.

63. The modified recombinant enzyme of paragraph 61, wherein the modified recombinant enzyme further comprises a bis-biotin tag.

64. The modified recombinant enzyme of paragraph 63, wherein the modified recombinant enzyme comprises the amino acid sequence of SEQ ID NO: 180.

65. A modified recombinant enzyme comprising one or more segments selected from: a first segment having an amino acid sequence that is at least 80%, 80-90%, 90-95%, or at least 95% identical to amino acids 1-196 of SEQ ID NO: 2, wherein the amino acid sequence of the first segment comprises a modification at one or more positions corresponding to K4, T13, S22, V25, C26, D27, N33, 134, F36, S42, D54, N59, E60, E65, E85, M95, N106, T110, T114, K119, Q122, Y133, P136, E139, E142, N145, P147, 1148, E152, 1153, P160, D167, D171, N175, F188, and D189 of SEQ ID NO: 2;

a second segment having an amino acid sequence that is at least 80%, 80-90%, 90-95%, or at least 95% identical to amino acids 197-271 of SEQ ID NO: 2, wherein the amino acid sequence of the second segment comprises a modification at one or more positions

corresponding to Q206, T211, S216, R217, D232, A236, V247, 1253, V261, L264, and S267 of SEQ ID NO: 2; and/or

a third segment having an amino acid sequence that is at least 80%, 80-90%, 90-95%, or at least 95% identical to amino acids 443-528 of SEQ ID NO: 2, wherein the amino acid sequence of the third segment comprises a modification at one or more positions corresponding to V443, L445, A446, S447, V449, T450, W452, G453, Y455, F465, N467, T479, E482, A484, E485, A486, L490, D492, S493, K495, K500, S503, Q506, Q513, E519, D521, E523, and V526 of SEQ ID NO: 2.

66. The modified recombinant enzyme of paragraph 65, wherein the modified recombinant enzyme comprises the first segment and the second segment.

67. The modified recombinant enzyme of paragraph 65, wherein the modified recombinant enzyme comprises the second segment and the third segment.

68. The modified recombinant enzyme of paragraph 65, wherein the modified recombinant enzyme comprises the first segment and the third segment.

69. The modified recombinant enzyme of paragraph 65, wherein the modified recombinant enzyme comprises the first segment, the second segment and the third segment.

70. The modified recombinant enzyme of any one of paragraphs 65-69, wherein a modification is an amino acid substitution selected from the group consisting of K4R, T13N, S22A, V25L, C26W, D27E, N33T, I34V, F36V, S42T, D54Y, N59D, E60L, E60V, E65S, E85P, M95T, M95K, N106G, T110I, T114S, K119Q, Q122V, Y133L, P136T, E139K, E139Q, E139R, E139H, E142K, E142Q, E142R, E142H, N145K, P147Q, P147T, I148K, I148H, I148R, E152D, I153V, P160A, D167P, D167K, D171K, D171H, D171R, N175T, F188C, D189K, D189H, D189R, Q206R, Q206K, Q206H, T211A, S216G, S216R, R217G, D232K, A236G, V247D, I253H, I253A, V261A, V261I, V261L, L264H, L264A, L264M, S267A, V443T, L445M, A446G, S447V, V449I, T450A, W452Y, G453A, Y455W, F465Y, N467R, N467K, N467H, N467S, N467T, T479V, E482K, E482H, E482R, A484E, E485D, A486E, L490M, D492H, D492K, D492R, D492A, H492S, S493P, K495R, K500E, S503A, S503T, Q506K, Q513D, D521K, D521R, D521H, E523R, E523V, E523Y, E523F, E523H, E523W, and V526L.

71. The modified recombinant enzyme of any one of paragraphs 65-70, wherein the amino acid sequence of the modified recombinant enzyme comprises a modification at one or more positions corresponding to E139, E142, N145, 1148, D167, D171, D189, N467, E482, D492, K495, D521, and E523.

72. The modified recombinant enzyme of paragraph 71, wherein a modification is an amino acid substitution selected from the group consisting of E139K, E139Q, E139R, E139H, E142K, E142H, E142R, E142Q, N145K, I148K, I148H, I148R, D167P, D167K, D171K,

D171H, D171R, D189K, D189H, D189R, N467R, N467K, N467H, N467S, N467T, E482K, E482H, E482R, D492H, D492K, D492R, K495R, D521K, D521H, D521R, E523K, E523Y, E523H, E523R, E523F, and E523W.

73. The modified recombinant enzyme of any one of paragraphs 65-72, wherein the amino acid sequence of the modified recombinant enzyme comprises a modification at one or more positions corresponding to P273, P275, R308, V315, Q317, S319, L320, 1322, Q323,

D337, E338, D341, T345, F352, F353, T364, D374, 1384, E385, N388, E391, A396, N397, G400, D414, D425, R429, E436, L437, D533, R534, E537, G547, E545, L555, P556, R558, T559, V564, T568, M569, and T571 of SEQ ID NO: 2.

74. The method of paragraph 73, wherein a modification is an amino acid substitution selected from the group consisting of P273S, P275S, E283K, V315L, S319R, R308G, G308R, Q317R, S319R, L320M, L320T, I322K, Q323G, Q323V, Q323R, D337G, E338K, D341T, T345I, F352I, F353C, T364I, D374G, I384T, I384F, I384S, E385Y, N388T, E391Y, E391W, E391F, E391H, E391M, E391K, E391R, A396Q, N397L, G400L, D414V, D425N, R429G, E436R, E436G, L437Y, L437E, D533A, R534K, E537K, E537H, E537R, E545K, G547S, L555K, L555R, P556A, R558H, T559V, V564L, T568D, T568S, M569K, M569T, M569V, and T571S.

75. The method of paragraph 73, wherein a modification is an amino acid substitution selected from the group consisting of D374G, E385Y, E391Y, E391W, E391K, E391F, D533A, E537K, E537H, E537R, and E545K.

76. The modified recombinant enzyme of any one of paragraphs 73-75, wherein the modified recombinant enzyme comprises a combination of modifications listed in Table 7.

77. The modified recombinant enzyme of any one of paragraphs 73-76, wherein the amino acid sequence of the modified recombinant enzyme comprises a modification at positions corresponding to E142, 1148, D189, V261, L264, R308, E391, E482, D492, K500, D521, E523, and E537.

78. The modified recombinant enzyme of paragraph 77, wherein:

the modification at position E142 is E142K;

the modification at position 1148 is I148K;

the modification at position D 189 is D189K;

the modification at position V261 is V261A;

the modification at position L264 is L264H;

the modification at position R308 is R308G;

the modification at position E391 is E391Y;

the modification at position E482 is E482K;

the modification at position D492 is D492H;

the modification at position K500 is K500E;

the modification at position D521 is D521K;

the modification at position E523 is E523K; and

the modification at position E537 is E537K.

79. The modified recombinant enzyme of paragraph 78, wherein the modified recombinant enzyme comprises the amino acid sequence of SEQ ID NO: 88.

80. The modified recombinant enzyme of paragraph 78, wherein the amino acid sequence of the modified recombinant enzyme comprises a modification at position E60.

81. The modified recombinant enzyme of paragraph 80, wherein the modification at E60 is E60L.

82. The modified recombinant enzyme of paragraph 81, wherein the modified recombinant enzyme comprises the amino acid sequence of SEQ ID NO: 157.

83. The modified recombinant enzyme of paragraph 81, wherein the modified recombinant enzyme further comprises a bis-biotin tag.

84. The modified recombinant enzyme of paragraph 83, wherein the modified recombinant enzyme comprises the amino acid sequence of SEQ ID NO: 180.

85. A modified recombinant enzyme comprising an amino acid sequence comprising: (i) a first segment, a second segment, a third segment, a fourth segment, a fifth segment, a sixth segment, and a seventh segment; and (ii) a modification at one or more positions corresponding to E139, E142, N145, 1148, D167, D171, D189, D374, E385, E391, N467, E482, D492, K495, D521, E523, D533, E537, and E545 of SEQ ID NO: 2; wherein the first segment comprises an amino acid sequence that is at least 80%, 80-90%, 90-95%, or at least 95% identical to a exonuclease region of a polymerizing enzyme of Table 1, Table 2, or Table 3;

the second segment and the sixth segment collectively comprise an amino acid sequence that is at least 80%, 80-90%, 90-95%, or at least 95% identical to a palm region of a polymerizing enzyme of Table 1, Table 2, or Table 3;

the third segment comprises an amino acid sequence that is at least 80%, 80-90%, 90-95%, or at least 95% identical to a TPR1 region of a polymerizing enzyme of Table 1, Table 2, or Table 3;

the fourth segment comprises an amino acid sequence that is at least 80%, 80- 90%, 90-95%, or at least 95% identical to a finger region of a polymerizing enzyme of Table 1, Table 2, or Table 3;

the fifth segment comprises an amino acid sequence that is at least 80%, 80-90%, 90-95%, or at least 95% identical to a TPR2 region of a polymerizing enzyme of Table 1, Table 2, or Table 3; and

the seventh segment comprises an amino acid sequence that is at least 80%, 80- 90%, 90-95%, or at least 95% identical to a thumb region of a polymerizing enzyme of Table 1, Table 2, or Table 3. In particular embodiments, a polymerizing enzyme from Table 1 is selected from any one of SEQ ID Nos.: 2-5. In some embodiments, a polymerizing enzyme from Table 1 is selected from any one of SEQ ID Nos: 23-33.

86. The modified recombinant enzyme of paragraph 85, wherein a modification is an amino acid substitution selected from the group consisting of E139K, E139Q, E139R, E139H, E142K, E142H, E142R, E142Q, N145K, I148K, I148H, I148R, D167P, D167K, D171K,

D171H, D171R, D189K, D189H, D189R, D374G, E385Y, E391Y, E391W, E391K, E391F, N467R, N467K, N467H, N467S, N467T, E482K, E482H, E482R, D492H, D492K, D492R, K495R, D521K, D521H, D521R, E523K, E523Y, E523H, E523R, E523F, E523W, D533A, E537K, E537H, E537R, and E545K.

87. The modified recombinant enzyme of paragraph 85 or 86, further comprising a modification at one or more positions corresponding to K4, T13, S22, V25, C26, D27, N33, 134, F36, S42, D54, N59, E60, E65, E85, M95, N106, T110, T114, K119, Q122, Y133, P136, P147, E152, 1153, PI 60, N175, F188, Q206, T211, S216, R217, D232, A236, V247, 1253, V261, L264, S267, P273, P275, R308, V315, Q317, S319, L320, 1322, Q323, D337, E338, D341, T345, F352, F353, T364, 1384, N388, A396, N397, G400, D414, D425, R429, E436, L437, V443, L445, A446, S447, V449, T450, W452, G453, Y455, F465, T479, A484, E485, A486, L490, S493, K500, S503, Q506, Q513, E519, V526, R534, G547, L555, P556, R558, T559, V564, T568, M569, and T571 of SEQ ID NO: 2.

88. The modified recombinant enzyme of paragraph 87, wherein a modification is an amino acid substitution selected from the group consisting of K4R, T13N, S22A, V25L, C26W, D27E, N33T, I34V, F36V, S42T, D54Y, N59D, E60L, E60V, E65S, E85P, M95T, M95K, N106G, T110I, T114S, K119Q, Q122V, Y133L, P136T, P147Q, P147T, E152D, I153V, P160A, N175T, F188C, Q206R, Q206K, Q206H, T211A, S216G, S216R, R217G, D232K, A236G, V247D, I253H, I253A, V261A, V261I, V261L, L264H, L264A, L264M, S267A, P273S, P275S, E283K, V315L, S319R, R308G, G308R, Q317R, S319R, L320M, L320T, I322K, Q323G, Q323V, Q323R, D337G, E338K, D341T, T345I, F352I, F353C, T364I, I384T, I384F, I384S, N388T, A396Q, N397L, G400L, D414V, D425N, R429G, E436R, E436G, L437Y, L437E, V443T, L445M, A446G, S447V, V449I, T450A, W452Y, G453A, Y455W, F465Y, T479V, A484E, E485D, A486E, L490M, S493P, K500E, S503A, S503T, Q506K, Q513D, V526L, R534K, G547S, L555K, L555R, P556A, R558H, T559V, V564L, T568D, T568S, M569K, M569T, M569V, and T571S.

89. The modified recombinant enzyme of paragraph 87 or 88, wherein the modified recombinant enzyme comprises a combination of modifications listed in Table 7.

90. A modified recombinant enzyme comprising:

an amino acid sequence this is at least 60%, 60-70%, 70-80%, or at least 80% identical to SEQ ID NO: 2; and

an extended palm domain, wherein the extended palm domain comprises an addition of an amino acid sequence that is at least 80%, 80-90%, 90-95%, or at least 95% identical to amino acids 505-524 of SEQ ID NO: 1.

91. The modified recombinant enzyme of paragraph 90 further comprising a modification at one or more positions corresponding to K4, T13, S22, V25, C26, D27, N33, 134, F36, S42, D54, N59, E60, E65, E85, M95, N106, T110, T114, K119, Q122, Y133, P136, E139, E142, N145, P147, 1148, E152, 1153, P160, D167, D171, N175, F188, D189, Q206, T211, S216, R217, D232, A236, V247, 1253, V261, L264, S267, V443, L445, A446, S447, V449, T450, W452, G453, Y455, F465, N467, T479, E482, A484, E485, A486, L490, D492, S493, K495, K500, S503, Q506, Q513, E519, D521, E523, and V526 of SEQ ID NO: 2.

92. The modified recombinant enzyme of paragraph 91, wherein a modification is an amino acid substitution selected from the group consisting of K4R, T13N, S22A, V25L, C26W, D27E, N33T, I34V, F36V, S42T, D54Y, N59D, E60L, E60V, E65S, E85P, M95T, M95K, N106G, T110I, T114S, K119Q, Q122V, Y133L, P136T, E139K, E139Q, E139R, E139H, E142K, E142Q, E142R, E142H, N145K, P147Q, P147T, I148K, I148H, I148R, E152D, I153V, P160A, D167P, D167K, D171K, D171H, D171R, N175T, F188C, D189K, D189H, D189R, Q206R, Q206K, Q206H, T211A, S216G, S216R, R217G, D232K, A236G, V247D, I253H, I253A, V261A, V261I, V261L, L264H, L264A, L264M, S267A, V443T, L445M, A446G, S447V, V449I, T450A, W452Y, G453A, Y455W, F465Y, N467R, N467K, N467H, N467S, N467T, T479V, E482K, E482H, E482R, A484E, E485D, A486E, L490M, D492H, D492K, D492R, D492A, H492S, S493P, K495R, K500E, S503A, S503T, Q506K, Q513D, D521K, D521R, D521H, E523R, E523V, E523Y, E523F, E523H, E523W, and V526L.

93. The modified recombinant enzyme of paragraph 91 or 92, wherein the amino acid sequence of the modified recombinant enzyme further comprises a modification at one or more positions corresponding to E139, E142, N145, 1148, D167, D171, D189, N467, E482, D492, K495, D521, and E523.

94. The modified recombinant enzyme of paragraph 93, wherein a modification is an amino acid substitution selected from the group consisting of E139K, E139Q, E139R, E139H, E142K, E142H, E142R, E142Q, N145K, I148K, I148H, I148R, D167P, D167K, D171K,

D171H, D171R, D189K, D189H, D189R, N467R, N467K, N467H, N467S, N467T, E482K, E482H, E482R, D492H, D492K, D492R, K495R, D521K, D521H, D521R, E523K, E523Y, E523H, E523R, E523F, and E523W.

95. The modified recombinant enzyme of any one of paragraphs 91-94, wherein the amino acid sequence of the modified recombinant enzyme comprises a modification at one or more positions corresponding to P273, P275, R308, V315, Q317, S319, L320, 1322, Q323,

D337, E338, D341, T345, F352, F353, T364, D374, 1384, E385, N388, E391, A396, N397, G400, D414, D425, R429, E436, L437, D533, R534, E537, G547, E545, L555, P556, R558, T559, V564, T568, M569, and T571 of SEQ ID NO: 2.

96. The method of paragraph 95, wherein a modification is an amino acid substitution selected from the group consisting of P273S, P275S, E283K, V315L, S319R, R308G, G308R, Q317R, S319R, L320M, L320T, I322K, Q323G, Q323V, Q323R, D337G, E338K, D341T, T345I, F352I, F353C, T364I, D374G, I384T, I384F, I384S, E385Y, N388T, E391Y, E391W, E391F, E391H, E391M, E391K, E391R, A396Q, N397L, G400L, D414V, D425N, R429G, E436R, E436G, L437Y, L437E, D533A, R534K, E537K, E537H, E537R, E545K, G547S, L555K, L555R, P556A, R558H, T559V, V564L, T568D, T568S, M569K, M569T, M569V, and T571S. 97. The method of paragraph 95, wherein a modification is an amino acid substitution selected from the group consisting of D374G, E385Y, E391Y, E391W, E391K, E391F, D533A, E537K, E537H, E537R, and E545K.

98. The modified recombinant enzyme of any one of paragraphs 95-97, wherein the modified recombinant enzyme comprises a combination of modifications listed in Table 7.

99. A modified recombinant enzyme having an amino acid sequence that is at least 60%, 60-70%, 70-80%, or at least 80% identical to any one of SEQ ID NOs: 1-33, wherein the amino acid sequence comprises a modification at one or more positions corresponding to K4, T13, S22, V25, C26, D27, N33, 134, F36, S42, D54, N59, E60, E65, E85, M95, N106, T110, T114, K119, Q122, Y133, P136, E139, E142, N145, P147, 1148, E152, 1153, P160, D167, D171, N175, F188, D189, Q206, T211, S216, R217, D232, A236, V247, 1253, V261, L264, S267,

P273, P275, R308, V315, Q317, S319, L320, 1322, Q323, D337, E338, D341, T345, F352, F353, T364, D374, 1384, E385, N388, E391, A396, N397, G400, D414, D425, R429, E436, L437, V443, L445, A446, S447, V449, T450, W452, G453, Y455, F465, N467, T479, E482, A484, E485, A486, L490, D492, S493, K495, K500, S503, Q506, Q513, E519, D521, E523, V526, D533, R534, E537, G547, E545, L555, P556, R558, T559, V564, T568, M569, and T571 of E. faecium polymerase (SEQ ID NO: 2). In particular embodiments, a modified recombinant enzyme has an amino acid sequence that is at least 60%, 60-70%, 70-80%, or at least 80% identical to any one of SEQ ID NOs: 2-5 and comprises a modification at one or more of the positions. In a particular embodiment, a modified recombinant enzyme is a modified E. faecium polymerase that has an amino acid sequence that is at least 60%, 60-70%, 70-80%, or at least 80% identical to any one of SEQ ID NO: 2 and comprises a modification at one or more of the positions. In a particular embodiments, a modified recombinant enzyme is a modified E. faecium polymerase that comprises the amino acid sequence of SEQ ID NO: 2 and comprises a modification at one or more of the positions. In some embodiments, a modified recombinant enzyme has an amino acid sequence that is 60%, 60-70%, 70-80%, or at least 80% identical to any one of SEQ ID NOs: 23-33, and comprises a modification at one or more of the positions.

100. The modified recombinant enzyme of paragraph 99, comprising a modification at one or both positions corresponding to T568 and M569 of SEQ ID NO: 2.

101. The modified recombinant enzyme of paragraph 100, wherein a modification is an amino acid substitution selected from the group consisting of T568D, T568S, M569T, and M569V. 102. The modified recombinant enzyme of paragraph 100 or paragraph 101, wherein the modified recombinant enzyme has improved processivity relative to E. faecium polymerase (SEQ ID NO: 2).

103. The modified recombinant enzyme of any one of paragraphs 99-102, comprising a modification at a position corresponding to N59 of SEQ ID NO: 2.

104. The modified recombinant enzyme of paragraph 103, wherein the modification is

N59D.

105. The modified recombinant enzyme of paragraph 103 or paragraph 104, wherein the modified recombinant enzyme has altered exonuclease activity relative to E. faecium polymerase (SEQ ID NO: 2).

106. The modified recombinant enzyme of any one of paragraphs 99-105, comprising a modification at one or more positions corresponding to V261, L264, S267, 1384, E391, W452, G453, Y455, D492, and K500 of SEQ ID NO: 2.

107. The modified recombinant enzyme of paragraph 106, wherein a modification is an amino acid substitution selected from the group consisting of V261A, V261I, L264A, L264H, L264M, S267A, I384F, I384S, E391Y, E391W, E391F, E391H, E391M, E391K, E391R, W452Y, G453A, Y455W, D492H, and K500E.

108. The modified recombinant enzyme of paragraph 106 or paragraph 107, wherein the modified recombinant enzyme has improved nucleotide substrate utilization relative to E. faecium polymerase (SEQ ID NO: 2).

109. The modified recombinant enzyme of any one of paragraphs 99-108, comprising a modification at one or more positions corresponding to E65, Y133, E391, G400, V443, L445, A446, S447, V449, T450, S503, E523, L555, and P556 of SEQ ID NO: 2.

110. The modified recombinant enzyme of paragraph 109, wherein a modification is an amino acid substitution selected from the group consisting of E65S, Y133L, E391Y, E391W, E391F, E391K, G400L, V443T, L445M, A446G, S447V, V449I, T450A, S503A, E523K, E523Y, E523F, E523H, E523W, L555K, and P556A.

111. The modified recombinant enzyme of paragraph 109 or paragraph 110, wherein the modified recombinant enzyme has improved accuracy relative to E. faecium polymerase (SEQ ID NO: 2).

112. The modified recombinant enzyme of any one of paragraphs 99-111, comprising a modification at one or more positions corresponding to Q317, S319, 1322, Q323, R429, L555, and T559 of SEQ ID NO: 2. 113. The modified recombinant enzyme of paragraph 112, wherein a modification is an amino acid substitution selected from the group consisting of Q317R, S319R, I322K, Q323G, R429G, L555K, and T559V.

114. The modified recombinant enzyme of paragraph 112 or paragraph 113, wherein the modified recombinant enzyme has an increased DNA-binding affinity relative to E. faecium polymerase (SEQ ID NO: 2).

115. The modified recombinant enzyme of any one of paragraphs 99-114, comprising a modification at one or more positions corresponding to E391, S503 and E523 of SEQ ID NO: 2.

116. The modified recombinant enzyme of paragraph 115, wherein a modification is an amino acid substitution selected from the group consisting of E391Y, E391W, E391F, E391K, S503A, E523K, E523Y, E523F, E523H, and E523W.

117. The modified recombinant enzyme of paragraph 115 or paragraph 116, wherein the modified recombinant enzyme has an increased analog-binding affinity relative to E. faecium polymerase (SEQ ID NO: 2).

118. The modified recombinant enzyme of any one of paragraphs 99-117, comprising a modification at one or more positions corresponding to Q206, E436 and L437 of SEQ ID NO: 2.

119. The modified recombinant enzyme of paragraph 118, wherein a modification is an amino acid substitution selected from the group consisting of Q206R, Q206K, Q206H, E436R, L437Y, and L437E.

120. The modified recombinant enzyme of paragraph 118 or paragraph 119, wherein the modified recombinant enzyme has improved strand displacement relative to E. faecium polymerase (SEQ ID NO: 2).

121. The modified recombinant enzyme of any one of paragraphs 99-120, comprising a modification at one or more positions corresponding to E436, L437, R534, T568, and M569 of SEQ ID NO: 2.

122. The modified recombinant enzyme of paragraph 121, wherein a modification is an amino acid substitution selected from the group consisting of E436R, L437Y, L437E, R534K, T568D, T568S, M569T, and M569V.

123. The modified recombinant enzyme of paragraph 121 or paragraph 122, wherein the modified recombinant enzyme has an enhanced average read length relative to E. faecium polymerase (SEQ ID NO: 2).

124. The modified recombinant enzyme of any one of paragraphs 99-123, comprising a modification at one or more positions corresponding to T13, V25, C26, D27, N33, 134, F36, S42, D54, M95, T110, T114, K119, P136, P147, E152, 1153, P160, N175, F188, S216, R217, D232, A236, V247, P273, E283, V315, S319, L320, Q323, E338, T345, F352, F353, T364, D414, D425, E436, F465, E485, A486, L490, S503, E523, V526, G547, L555, R558,V564, M569, and T571 of SEQ ID NO: 2.

125. The modified recombinant enzyme of paragraph 124, wherein a modification is an amino acid substitution selected from the group consisting of T13N, V25L, C26W, D27E, N33T, I34V, F36V, S42T, D54Y, M95T, M95K, T110I, T114S, K119Q, P136T, P147Q, P147T,

E152D, I153V, P160A, N175T, F188C, S216G, S216R, R217G, D232H, A236G, V247D,

P273S, E283K, V315L, S319R, L320M, L320T, Q323R, E338K, T345I, F352I, F353C, T364I, D414V, D425N, E436G, F465Y, E485D, A486E, L490M, S503T, E523V, V526L, G547S, L555R, R558H, V564L, M569K, and T571S.

126. The modified recombinant enzyme of paragraph 124 or paragraph 125, wherein the modified recombinant enzyme has an increased replication capacity relative to E. faecium polymerase (SEQ ID NO: 2).

127. The modified recombinant enzyme of any one of paragraphs 99-126, comprising a modification at one or more positions corresponding to E139, E142, N145, 1148, D167, D171, D189, D374, E385, E391, N467, E482, D492, K495, D521, E523, D533, E537, and E545 of SEQ ID NO: 2.

128. The modified recombinant enzyme of paragraph 127, wherein a modification is an amino acid substitution selected from the group consisting of E139K, E139Q, E139R, E139H, E142K, E142H, E142R, E142Q, N145K, I148K, I148H, I148R, D167P, D167K, D171K, D171H, D171R, D189K, D189H, D189R, D374G, E385Y, E391Y, E391W, E391K, E391F, N467R, N467K, N467H, N467S, N467T, E482K, E482H, E482R, D492H, D492K, D492R, K495R, D521K, D521H, D521R, E523K, E523Y, E523H, E523R, E523F, E523W, D533A, E537K, E537H, E537R, and E545K.

129. The modified recombinant enzyme of paragraph 127 or paragraph 128, wherein the modified recombinant enzyme has an increased electropositive surface charge relative to E. faecium polymerase (SEQ ID NO: 2).

130. The modified recombinant enzyme of any one of paragraphs 99-129, comprising a modification at one or more positions corresponding to K4, S22, D27, 134, D54, E60, E85, M95, N106, T110, Q122, Y133, P136, P147, D167, T211, D232, P275, R308, S319, L320, E323, D337, E338, D341, T345, F352, T364, D414, F465, T479, E485, L490, S493, Q513, and R558 of SEQ ID NO: 2.

131. The modified recombinant enzyme of paragraph 130, wherein a modification is an amino acid substitution selected from the group consisting of K4R, S22A, D27E, I34V, D54Y, E60V, E60L, E85P, M95K, T110I, N106G, Q122V, Y133L, P136T, P147Q, P147T, D167P, T211A, D232K, P275S, R308G, S319R, L320M, Q323V, D337G, E338K, D341T, T345I,

F352I, T364I, D414V, F465Y, T479V, E485D, L490M, S493P, Q513D, and R558H.

132. The modified recombinant enzyme of paragraph 130 or paragraph 131, wherein the modified recombinant enzyme has an increased stability relative to E. faecium polymerase (SEQ ID NO: 2).

133. The modified recombinant enzyme of any one of paragraphs 99-132, wherein the modified recombinant enzyme comprises a combination of modifications listed in Table 7.

134. A composition comprising the modified recombinant enzyme of any one of paragraphs 46-133.

135. A method of sequencing a nucleic acid, the method comprising contacting the modified recombinant enzyme of any one of paragraphs 46-133 with a sequencing reaction mixture.

All of the features disclosed in this specification may be combined in any combination. Each feature disclosed in this specification may be replaced by an alternative feature serving the same, equivalent, or similar purpose. Thus, unless expressly stated otherwise, each feature disclosed is only an example of a generic series of equivalent or similar features.

From the above description, one skilled in the art can easily ascertain the essential characteristics of the present invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. Thus, other embodiments are also within the claims.

EQUIVALENTS AND SCOPE

While several inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.

All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms.

All references, patents, and patent applications disclosed herein are incorporated by reference with respect to the subject matter for which each is cited, which in some cases may encompass the entirety of the document.

The indefinite articles“a” and“an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean“at least one.”

The phrase“and/or,” as used herein in the specification and in the claims, should be understood to mean“either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with“and/or” should be construed in the same fashion, i.e.,“one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the“and/or” clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to“A and/or B”, when used in conjunction with open-ended language such as“comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

As used herein in the specification and in the claims,“or” should be understood to have the same meaning as“and/or” as defined above. For example, when separating items in a list, “or” or“and/or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as“only one of’ or“exactly one of,” or, when used in the claims,“consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term“or” as used herein shall only be interpreted as indicating exclusive alternatives ( i.e .“one or the other but not both”) when preceded by terms of exclusivity, such as“either,”“one of,”“only one of,” or“exactly one of.”“Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase“at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase“at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example,“at least one of A and B” (or, equivalently,“at least one of A or B,” or, equivalently“at least one of A and/or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

It should also be understood that, unless clearly indicated to the contrary, in any methods claimed herein that include more than one step or act, the order of the steps or acts of the method is not necessarily limited to the order in which the steps or acts of the method are recited.

In the claims, as well as in the specification above, all transitional phrases such as “comprising,”“including,”“carrying,”“having,� �“containing,”“involving,”“holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases“consisting of’ and“consisting essentially of’ shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03. It should be appreciated that embodiments described in this document using an open-ended transitional phrase (e.g., “comprising”) are also contemplated, in alternative embodiments, as“consisting of’ and “consisting essentially of’ the feature described by the open-ended transitional phrase. For example, if the disclosure describes“a composition comprising A and B,” the disclosure also contemplates the alternative embodiments“a composition consisting of A and B” and“a composition consisting essentially of A and B.”