POTTER JASON (US)
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WO1998047912A1 | 1998-10-29 | |||
WO2006081222A2 | 2006-08-03 |
US5338671A | 1994-08-16 | |||
US5773258A | 1998-06-30 | |||
US5677152A | 1997-10-14 | |||
US4889818A | 1989-12-26 | |||
US4965188A | 1990-10-23 | |||
US5374553A | 1994-12-20 | |||
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US8753845B2 | 2014-06-17 | |||
US5668005A | 1997-09-16 | |||
US6063608A | 2000-05-16 | |||
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USPP18945400P | 2000-03-15 | |||
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EP0534858A1 | 1993-03-31 | |||
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See also references of EP 3097190A2
CLAIMS 1. An isolated mutant M‐MLV reverse transcriptase, comprising at least one mutation at an amino acid position selected from the group consisting of S67, T197, and E302 of wild type M‐MLV reverse transcriptase (SEQ ID NO:2).
2. The mutant M‐MLV reverse transcriptase of claim 1, comprising at least one mutation selected from the group consisting of: S67R, S67N, S67K, T197A, T197S, T197G, E302K, E302R, and E302G.
3. The mutant M‐MLV reverse transcriptase of claim 1, wherein said mutant reverse transcriptase further comprises at least one mutation at an amino acid position selected from the group consisting of: P51, E69, P196, D200, H204, M289, T306, F309, W313, T330, L435, N454, D524, E562, D583, H594, L603, D653, and L671 of wild type M‐MLV reverse transcriptase (SEQ ID NO:2).
4. The mutant M‐MLV reverse transcriptase of claim 3, comprising at least one mutation selected from the group consisting of: P51L, E69K, P196S, D200N, H204R, M289L, T306K, F309N, F309Y, F309I, W313F, W313L, W313C, T330P, L435G, L435V, L435R, N454K, D524G, E562Q, D583N, H594Q, L603W, D653N, D653H and L671P.
5. The mutant M‐MLV reverse transcriptase of claim 3, having a mutation at each amino acid position selected from the group consisting of: P51, S67, E69, T197, H204, E302, F309, W313, T330, L435, N454, D524, D583, H594, D653, and L671 of wild type M‐MLV reverse transcriptase (SEQ ID NO:2).
6. The mutant M‐MLV reverse transcriptase of claim 5, comprising the following mutations: P51L, S67R, E69K, T197A, H204R, E302K, F309N, W313F, T330P, L435G, N454K, D524G, D583N, H594Q, D653N, and L671P.
7. The mutant M‐MLV reverse transcriptase of claim 1, wherein said mutant reverse transcriptase lacks RNase H activity.
8. The mutant M‐MLV reverse transcriptase of claim 1, wherein said mutant reverse transcriptase possesses one or more of the following properties: a. thermostability; b. thermoreactivity; c. increased resistance to reverse transcriptase inhibitors; d. increased ability to reverse transcribe difficult templates e. increased speed; f. increased processivity; g. increased specificity; or h. increased sensitivity.
9. The mutant M‐MLV reverse transcriptase of claim 8, wherein said mutant reverse transcriptase is thermoreactive.
10. The mutant M‐MLV reverse transcriptase of claim 1, wherein said mutant reverse transcriptase synthesizes at least 50% more reverse transcriptase product within 5 minutes at 60°C than the amount of reverse transcriptase product synthesized by wild type M‐MLV after 5 minutes at 37°C.
11. The mutant M‐MLV reverse transcriptase of claim 1, wherein said mutant reverse transcriptase synthesizes at least 75% more reverse transcriptase product within 5 minutes at 60°C than the amount of reverse transcriptase product synthesized by wild type M‐MLV after 5 minutes at 37°C.
12. The mutant M‐MLV reverse transcriptase of claim 1, wherein said mutant reverse transcriptase synthesizes at least 100% more reverse transcriptase product within 5 minutes at 60°C than the amount of reverse transcriptase product synthesized by wild type M‐MLV after 5 minutes at 37°C.
13. The mutant M‐MLV reverse transcriptase of claim 1, wherein said mutant reverse transcriptase synthesizes at least 200% more reverse transcriptase product within 5 minutes
at 60°C than the amount of reverse transcriptase product synthesized by wild type M‐MLV after 5 minutes at 37°C.
14. The mutant M‐MLV reverse transcriptase of claim 1, wherein said mutant reverse transcriptase demonstrates increased reverse transcriptase activity at a reaction temperature of 60°C compared to reverse transcriptase activity of said wild type M‐MLV reverse transcriptase.
15. The mutant M‐MLV reverse transcriptase of claim 14, wherein said increased reverse transcriptase activity is at least 50% more compared to wild type M‐MLV reverse transcriptase activity.
16. The mutant M‐MLV reverse transcriptase of claim 14, wherein said increased reverse transcriptase activity is at least 75% more compared to wild type M‐MLV reverse transcriptase activity.
17. The mutant M‐MLV reverse transcriptase of claim 14, wherein said increased reverse transcriptase activity is at least 100% more compared to wild type M‐MLV reverse transcriptase activity.
18. The mutant M‐MLV reverse transcriptase of claim 14, wherein said increased reverse transcriptase activity is at least 200% more compared to wild type M‐MLV reverse transcriptase activity.
19. An isolated mutant M‐MLV reverse transcriptase, comprising at least six mutations at an amino acid position selected from the group consisting of P51, E69, P196, D200, H204, M289, T306, F309, W313, T330, L435, N454, D524, E562, D583, H594, L603, D653, and L671 of wild type M‐MLV (SEQ ID NO:2).
20. The mutant M‐MLV reverse transcriptase of claim 19, comprising at least six mutations selected from the group consisting of P51L, E69K, P196S, D200N, H204R, M289L, T306K,
F309N, F309Y, F309I, W313F, W313L, W313C, T330P, L435G, L435V, L435R, N454K, D524G, E562Q, D583N, H594Q, L603W, D653N, D653H and L671P.
21. The mutant M‐MLV reverse transcriptase of claim 19, wherein said mutant reverse transcriptase further comprises at least one mutation at an amino acid position selected from the group consisting of S67, T197, and E302 of wild type M‐MLV (SEQ ID NO:2). 22. The mutant M‐MLV reverse transcriptase of claim 21, wherein said reverse transcriptase comprises at least one mutation selected from the group consisting of S67R, S67N, S67K, T197A, T197S, T197G, E302K, E302R, and E302G.
23. The mutant M‐MLV reverse transcriptase of claim 19, wherein said mutant reverse transcriptase lacks RNase H activity.
24. The mutant M‐MLV reverse transcriptase of claim 19, wherein said increased reverse transcriptase activity comprises one or more of the following: a. increased thermostability; b. increased thermoreactivity; c. increased resistance to reverse transcriptase inhibitors; d. increased ability to reverse transcribe difficult templates e. increased speed; f. increased processivity; g. increased specificity; and h. increased sensitivity.
25. The mutant M‐MLV reverse transcriptase of claim 24, wherein said mutant reverse transcriptase is thermoreactive.
26. The mutant M‐MLV reverse transcriptase of claim 19, wherein said mutant reverse transcriptase synthesizes at least 50% more reverse transcriptase product within 5 minutes at 60°C than the amount of reverse transcriptase product synthesized by wild type M‐MLV after 5 minutes at 37°C.
27. The mutant M‐MLV reverse transcriptase of claim 19, wherein said mutant reverse transcriptase synthesizes at least 75% more reverse transcriptase product within 5 minutes at 60°C than the amount of reverse transcriptase product synthesized by wild type M‐MLV after 5 minutes at 37°C.
28. The mutant M‐MLV reverse transcriptase of claim 19, wherein said mutant reverse transcriptase synthesizes at least 100% more reverse transcriptase product within 5 minutes at 60°C than the amount of reverse transcriptase product synthesized by wild type M‐MLV after 5 minutes at 37°C.
29. The mutant M‐MLV reverse transcriptase of claim 19, wherein said mutant reverse transcriptase synthesizes at least 200% more reverse transcriptase product within 5 minutes at 60°C than the amount of reverse transcriptase product synthesized by wild type M‐MLV after 5 minutes at 37°C.
30. The mutant M‐MLV reverse transcriptase of claim 19, wherein said mutant reverse transcriptase demonstrates increased reverse transcriptase activity at a reaction temperature of 60°C compared to reverse transcriptase activity of said wild type M‐MLV reverse transcriptase.
31. The mutant M‐MLV reverse transcriptase of claim 19, wherein said increased reverse transcriptase activity is at least 50% more compared to wild type M‐MLV reverse transcriptase activity.
32. The mutant M‐MLV reverse transcriptase of claim 19, wherein said increased reverse transcriptase activity is at least 75% more compared to wild type M‐MLV reverse transcriptase activity.
33. The mutant M‐MLV reverse transcriptase of claim 19, wherein said increased reverse transcriptase activity is at least 100% more compared to wild type M‐MLV reverse transcriptase activity.
34. The mutant M‐MLV reverse transcriptase of claim 19, wherein said increased reverse transcriptase activity is at least 200% more compared to wild type M‐MLV reverse transcriptase activity.
35. An isolated mutant reverse transcriptase, wherein said mutant reverse transcriptase comprises at least 95% amino acid sequence identity to SEQ ID NO:4.
36. The mutant reverse transcriptase of claim 35, comprising SEQ ID NO:4.
37. The mutant reverse transcriptase of claim 35, consisting of SEQ ID NO:4.
38. The mutant reverse transcriptase of claim 35, wherein said mutant reverse transcriptase is thermostable at 60°C.
39. The mutant reverse transcriptase of claim 35, wherein said mutant reverse transcriptase is thermostable at 60°C for at least 5 minutes.
40. The mutant reverse transcriptase of claim 35, wherein said mutant reverse transcriptase is thermoreactive at 60°C for at least 5 minutes.
41. The mutant reverse transcriptase of claim 40, wherein said mutant reverse transcriptase is thermoreactive at 60°C for at least 15 minutes.
42. An isolated M‐MLV reverse transcriptase which has been mutated to increase or enhance thermostability compared to wild type M‐MLV reverse transcriptase, wherein said mutant reverse transcriptase comprises at least one mutation selected from the group consisting of: a. S67R; b. T197A; and c. E302K.
43. The reverse transcriptase of claim 42, further comprising at least one mutation selected from the group consisting of: a. P51L; b. E69K; c. H204R; d. F309N; e. W313F; f. T330P; g. L435G; h. N454K; i. D524G; j. D583N; k. H594Q; l. D653N; and m. L671P.
44. The reverse transcriptase of claim 42, wherein said reverse transcriptase retains at least 50% reverse transcriptase activity after heating to 45°C for 1 minute.
45. The reverse transcriptase of claim 42, wherein said reverse transcriptase retains at least 50% reverse transcriptase activity after heating to 50°C for 1 minute.
46. The reverse transcriptase of claim 42, wherein said reverse transcriptase retains at least 50% reverse transcriptase activity after heating to 55°C for 1 minute.
47. The reverse transcriptase of claim 42, wherein said reverse transcriptase retains at least 50% reverse transcriptase activity after heating to 60°C for 1 minute.
48. The reverse transcriptase of claim 42, wherein said reverse transcriptase retains at least 70% reverse transcriptase activity after heating to 60°C for 1 minute.
49. The reverse transcriptase of claim 42, wherein said reverse transcriptase retains at least 80% reverse transcriptase activity after heating to 60°C for 1 minute.
50. The reverse transcriptase of claim 42, wherein said reverse transcriptase retains at least 90% reverse transcriptase activity after heating to 60°C for 1 minute.
51. The reverse transcriptase of claim 42, wherein said reverse transcriptase retains at least 50% reverse transcriptase activity after heating to 50°C for 5 minutes.
52. The reverse transcriptase of claim 42, wherein said reverse transcriptase retains at least 50% reverse transcriptase activity after heating to 50°C for 15 minutes.
53. The reverse transcriptase of claim 42, wherein said reverse transcriptase retains at least 50% reverse transcriptase activity after heating to 50°C for 60 minutes.
54. An isolated M‐MLV reverse transcriptase which has been mutated to increase or enhance thermostability compared to wild type M‐MLV reverse transcriptase, wherein said mutant reverse transcriptase comprises at least six mutations selected from the group consisting of: a. P51L; b. E69K; c. H204R; d. F309N; e. W313F; f. T330P; g. L435G; h. N454K; i. D524G; j. D583N; k. H594Q; l. D653N; and m. L671P.
55. The reverse transcriptase of claim 54, further comprising at least one mutation selected from the group consisting of: a. S67R; b. T197A; and c. E302K.
56. The reverse transcriptase of claim 54, wherein said reverse transcriptase retains at least 50% reverse transcriptase activity after heating to 45°C for 1 minute.
57. The reverse transcriptase of claim 54, wherein said reverse transcriptase retains at least 50% reverse transcriptase activity after heating to 50°C for 1 minute.
58. The reverse transcriptase of claim 54, wherein said reverse transcriptase retains at least 50% reverse transcriptase activity after heating to 55°C for 1 minute.
59. The reverse transcriptase of claim 54, wherein said reverse transcriptase retains at least 50% reverse transcriptase activity after heating to 60°C for 1 minute.
60. The reverse transcriptase of claim 54, wherein said reverse transcriptase retains at least 70% reverse transcriptase activity after heating to 60°C for 1 minute.
61. The reverse transcriptase of claim 54, wherein said reverse transcriptase retains at least 80% reverse transcriptase activity after heating to 60°C for 1 minute.
62. The reverse transcriptase of claim 54, wherein said reverse transcriptase retains at least 90% reverse transcriptase activity after heating to 60°C for 1 minute.
63. The reverse transcriptase of claim 54, wherein said reverse transcriptase retains at least 50% reverse transcriptase activity after heating to 50°C for 5 minutes.
64. The reverse transcriptase of claim 54, wherein said reverse transcriptase retains at least 50% reverse transcriptase activity after heating to 50°C for 15 minutes.
65. The reverse transcriptase of claim 54, wherein said reverse transcriptase retains at least 50% reverse transcriptase activity after heating to 50°C for 60 minutes.
66. An isolated mutant reverse transcriptase, wherein said reverse transcriptase is able to produce a cDNA that is at least 7.5 kb within 5 minutes at 60°C.
67. An isolated mutant reverse transcriptase, wherein said reverse transcriptase is able to produce a cDNA that is at least 9.5 kb within 15 minutes at 60°C.
68. An isolated mutant reverse transcriptase, wherein said reverse transcriptase is thermostable at 60°C for at least 5 minutes.
69. The mutant reverse transcriptase of claim 68, wherein said mutant reverse transcriptase is thermostable at 60°C for at least 15 minutes.
70. The mutant reverse transcriptase of claim 68, wherein said mutant reverse transcriptase is thermostable at 60°C for at least 30 minutes.
71. An isolated mutant reverse transcriptase, wherein said reverse transcriptase is thermoreactive at 60°C for at least 5 minutes.
72. The mutant reverse transcriptase of claim 71, wherein said mutant reverse transcriptase is thermoreactive at 60°C for at least 15 minutes.
73. The mutant reverse transcriptase of claim 71, wherein said mutant reverse transcriptase is thermoreactive at 60°C for at least 30 minutes.
74. The mutant reverse transcriptase of any one of claims 66‐73, wherein said mutant reverse transcriptase is a mutant M‐MLV reverse transcriptase.
75. A composition for nucleic acid synthesis comprising a mutant M‐MLV reverse transcriptase and a buffer, wherein said mutant reverse transcriptase comprises at least one mutation at an amino acid position corresponding to the sequence for wild type M‐MLV reverse transcriptase (SEQ ID NO:2), wherein said at least one amino acid position is selected from the group consisting of: S67, T197, and E302.
76. The composition of claim 75, said composition further comprising one or more components selected from the group consisting of one or more nucleotides, one or more DNA polymerases, , one or more detergents, one or more primers, one or more hot start components, and one or more terminating agents.
77. The composition of claim 76, wherein said terminating agent is a dideoxynucleotide. 78. A composition for nucleic acid synthesis comprising a mutant M‐MLV reverse transcriptase and a buffer, wherein said mutant reverse transcriptase comprises at least six mutations at an amino acid position corresponding to the sequence for wild type M‐MLV reverse transcriptase (SEQ ID NO:2), wherein said at least six amino acid positions are selected from the group consisting of: P51, E69, H204, F309, W313, T330, L435, N454, D524, D583, H594, D653, and L671.
79. The composition of claim 78, said composition further comprising one or more components selected from the group consisting of one or more nucleotides, one or more DNA polymerases, , one or more detergents, one or more primers, one or more hot start components, and one or more terminating agents.
80. The composition of claim 79, wherein said terminating agent is a dideoxynucleotide. 81. A composition for nucleic acid synthesis, comprising a mutant M‐MLV reverse transcriptase and a buffer, wherein said mutant reverse transcriptase comprises at least 95% amino acid sequence identity to SEQ ID NO:4.
82. The composition of claim 81, said composition further comprising one or more components selected from the group consisting of one or more nucleotides, one or more DNA polymerases, , one or more detergents, one or more primers, one or more hot start components, and one or more terminating agents.
83. The composition of claim 82, wherein said terminating agent is a dideoxynucleotide. 84. A method for nucleic acid synthesis, comprising the use of a mutant M‐MLV reverse transcriptase having at least one mutation at an amino acid position corresponding to the sequence for wild type M‐MLV reverse transcriptase (SEQ ID NO:2), wherein said at least one amino acid position is selected from the group consisting of: S67, T197, and E302.
85. A method for reverse transcription of one or more nucleic acid molecules, said method comprising: a. preparing a mixture comprising one or more nucleic acid templates with one or more reverse transcriptases; and b. incubating said mixture under conditions sufficient to make one or more first nucleic acid molecules complementary to all or a portion of said one or more nucleic acid templates, wherein said one or more reverse transcriptases comprises at least one mutation at an amino acid position corresponding to the sequence for wild type M‐MLV reverse transcriptase (SEQ ID NO:2), wherein said at least one amino acid position is selected from the group consisting of: S67, T197, and E302.
86. The method of claim 85, wherein said nucleic acid template is a messenger RNA molecule or a population of mRNA molecules.
87. The method of claim 85, said method further comprising a step of incubating said one or more first nucleic acid molecules under conditions sufficient to make one or more second nucleic acid molecules complementary to all or a portion of said one or more first nucleic acid molecules.
88. The method of claim 85, wherein said incubating is performed at a temperature of about 60°C.
89. A method for amplifying one or more nucleic acid molecules, comprising: a. mixing one or more nucleic acid templates with one or more reverse transcriptases and one or more DNA polymerases; and b. incubating the mixture under conditions sufficient to amplify one or more nucleic acid molecules complementary to all or a portion of said one or more templates, wherein said one or more reverse transcriptases comprises at least one mutation at an amino acid position corresponding to the sequence for wild type M‐MLV reverse transcriptase (SEQ ID NO:2), wherein said at least one amino acid position is selected from the group consisting of: S67, T197, and E302.
90. The method of claim 89, wherein said incubating is performed at a temperature of about 60°C.
91. The method of claim 89, further comprising a step of determining the nucleotide sequence of all or a portion of said amplified nucleic acid molecules complementary to all or a portion of said one or more templates.
92. A method for nucleic acid synthesis, comprising the use of a mutant M‐MLV reverse transcriptase having at least one mutation at an amino acid position corresponding to the sequence for wild type M‐MLV reverse transcriptase (SEQ ID NO:2), wherein said at least six amino acid positions are selected from the group consisting of: P51, E69, H204, F309, W313, T330, L435, N454, D524, D583, H594, D653, and L671.
93. A method for reverse transcription of one or more nucleic acid molecules, said method comprising: a. preparing a mixture comprising one or more nucleic acid templates with one or more reverse transcriptases; and
b. incubating said mixture under conditions sufficient to make one or more first nucleic acid molecules complementary to all or a portion of said one or more nucleic acid templates, wherein said one or more reverse transcriptases comprises at least six mutations at an amino acid position corresponding to the sequence for wild type M‐MLV reverse transcriptase (SEQ ID NO:2), wherein said at least six amino acid positions are selected from the group consisting of: P51, E69, H204, F309, W313, T330, L435, N454, D524, D583, H594, D653, and L671.
94. The method of claim 93, wherein said nucleic acid template is a messenger RNA molecule or a population of mRNA molecules.
95. The method of claim 93, said method further comprising a step of incubating said one or more first nucleic acid molecules under conditions sufficient to make one or more second nucleic acid molecules complementary to all or a portion of said one or more first nucleic acid molecules.
96. The method of claim 93, wherein said incubating is performed at a temperature of about 60°C.
97. A method for amplifying one or more nucleic acid molecules, comprising: a. mixing one or more nucleic acid templates with one or more reverse transcriptases and one or more DNA polymerases; and b. incubating the mixture under conditions sufficient to amplify one or more nucleic acid molecules complementary to all or a portion of said one or more templates, wherein said one or more reverse transcriptases comprises at least six mutations at an amino acid position corresponding to the sequence for wild type M‐MLV reverse transcriptase (SEQ ID NO:2), wherein said at least six amino acid positions are selected from the group consisting of: P51, E69, H204, F309, W313, T330, L435, N454, D524, D583, H594, D653, and L671.
98. The method of claim 97, wherein said incubating is performed at a temperature of about 60°C.
99. The method of claim 97, further comprising a step of determining the nucleotide sequence of all or a portion of said amplified nucleic acid molecules complementary to all or a portion of said one or more templates.
100. A kit comprising a mutant M‐MLV reverse transcriptase in one or more packaged containers, wherein said mutant reverse transcriptase comprises at least one mutation at an amino acid position corresponding to the sequence for wild type M‐MLV reverse transcriptase (SEQ ID NO:2), wherein said at least one amino acid position is selected from the group consisting of: S67, T197, and E302.
101. A kit comprising a mutant M‐MLV reverse transcriptase in one or more packaged containers, wherein said mutant reverse transcriptase comprises at least six mutations at an amino acid position corresponding to the sequence for wild type M‐MLV reverse transcriptase (SEQ ID NO:2), wherein said at least six amino acid positions are selected from the group consisting of: P51, E69, H204, F309, W313, T330, L435, N454, D524, D583, H594, D653, and L671.
102. An isolated nucleic acid encoding a polypeptide with reverse transcriptase activity, wherein said polypeptide comprises an amino acid sequence that has at least 95% amino acid sequence identity to SEQ ID NO:4.
103. A vector comprising the nucleic acid of claim 102.
104. An expression vector comprising a promoter operably linked to the nucleic acid of claim 102.
105. A host cell comprising the nucleic acid of claim 102.
106. A host cell comprising the mutant reverse transcriptase of claim 35.
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[3] A factor that influences the efficiency of reverse t ranscription is the ability of RNA to form secondary structures. Such secondary structures can fo rm, for example, when regions of RNA molecules have sufficient complementarity to hybridize and form double stranded RNA. Generally, the formation of RNA secondary structures can be reduced by raising the temperature of solutions which contain the RNA molecu les. Thus, in many instances, it is desirable to reverse transcribe RNA at temperatures a bove 37°C. However, reverse transcriptases generally lose activity when incubated at temperatures much above 37°C (e.g., 50°C).
[4] The accuracy of methods utilizing reverse transcriptas es, including molecular diagnostics methods using such enzymes, would be improved by the discovery of reverse transcriptases with improved thermostability and/or thermoreactivity. If such enzymes were available, then methods employed for other thermostable enzymes to im prove accuracy, could be used to conceive new methods utilizing thermostable reverse tr anscriptases. For instance, ‘hot start’
approaches have been employed with thermostable pol ymerases to improve the accuracy of polymerase chain reaction (PCR) methods. In one examp le, U.S. Pat. No. 5,338,671 describes the use of antibodies specific for a thermostable DN A polymerase to inhibit the DNA polymerase activity at low temperatures (e.g. <70° C). Chemical treatment with citraconic anhydride is another way hot start PCR has been ach ieved (see, e.g., U.S. Pat. No. 5,773,258 and U.S. Pat. No. 5,677,152). The application of suc h hot start approaches to reverse transcription has proven to be challenging. This is because, for example, many reverse transcriptases are not heat‐stable.
[5] Moreover, biological samples from which nucleic acids are extracted often contain additional compounds that are inhibitory to reverse transcription . Humic acid in soil, plants and feces, hematin in blood, immunoglobin G in serum, and vario us blood anticoagulants, like heparin and citrate, are all examples of such inhibitors. Su ch inhibitors may not be completely removed during the nucleic acid extraction and purifi cation process, thus negatively impacting downstream nucleic acid synthesis, as reflec ted by a decrease in cDNA product produced as a result of reverse transcription.
[6] Thus, improved reverse transcriptases, and compositions , kits and methods that include such reverse transcriptases which overcome some of the dra wbacks mentioned above are met by the present invention. BRIEF SUMMARY OF THE INVENTION [7] The present invention provides mutant reverse transcri ptase enzymes with improved properties, and compositions, kits, and methods that include such novel enzymes.
Accordingly, the present invention provides, in certai n embodiments, mutant reverse transcriptase enzymes that exhibit increased thermostab ility, increased thermoreactivity, and/or increased speed, as well as additional benefic ial properties such as improved inhibitor resistance, for example resistance to polyphenol‐like compounds, improved cDNA generation with difficult RNA templates, and increased specificit y; and to methods of producing, such as by reverse transcribing, amplifying or sequencing nucl eic acid molecules, for example mRNA molecules, using such reverse transcriptase enzymes. In illustrative embodiments, mutant reverse transcriptases of the present invention includ e two or more of the aforementioned
properties. Mutant reverse transcriptases with other beneficial properties are provided herein, some of which include one or more of the a dditional aforementioned properties. In certain embodiments, the invention provides kits and compositions, such as storage compositions and reaction mixtures, which include the mutant reverse transcriptases provided herein.
[8] In certain illustrative embodiments, the mutant revers e transcriptases provide increased efficiency in reverse transcription, especially with r egard to reverse transcription carried out at elevated temperatures. Accordingly, in certain illu strative embodiments, the present invention provides mutant reverse transcriptases wherei n one or more amino acid changes have been made which renders the enzyme more thermos table and/or thermoreactive during nucleic acid synthesis reactions.
[9] In some embodiments, the present invention is directe d to mutant reverse transcriptases derived from Maloney Murine Leukemia Virus (M‐MLV) reverse transcriptase. In particular, the present invention provides reverse transcriptases having improved thermostability by substituting one or more amino acid residues of the wild type amino acid sequence of M‐ MLV reverse transcriptase represented by SEQ. ID. NO: 2 with other amino acid residues. In some embodiments, the amino acid positions targeted f or mutation or modification to produce higher thermostability and/or thermoreactivity (as well as other properties disclosed herein) are listed in Table 1. For examp le, the present invention includes M‐MLV reverse transcriptases having specific mutations (or c ombinations thereof) at amino acid positions corresponding to wild type M‐MLV selected from the group consisting of: P51, S67, E69, T197, H204, E302, F309, W313, T330, L435, N454, D524, D583, H594, D653, and/or L671. In a preferred embodiment of the present inv ention, M‐MLV reverse transcriptases are provided having all of the following mutations P 51L, S67R, E69K, T197A, H204R, E302K, F309N, W313F, T330P, L435G, N454K, D524G, D583N, H594 Q, D653N, and L671P. In some embodiments, reverse transcriptases of the invention a lso preferably have reduced or substantially reduced RNase H activity.
[10] Similar or equivalent sites of corresponding amino ac id positions in reverse
transcriptases from other species can be mutated to produce thermostable and/or thermoreactive reverse transcriptases as disclosed here in. For example, in some
embodiments the present invention provides reverse tra nscriptases having at least 50% (e.g.,
50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91% , 92%, 93%, 94%, 95%, 96%, etc.) amino acid sequence identity to SEQ ID NO:4.
[11] In some embodiments, the mutant M‐MLV reverse trans criptases of the present invention exhibit increased reverse transcriptases acti vity at a reaction temperature of at least 50°C (e.g., 50°C, 55°C, 60°C, 65°C, 70°C, and 75°C) when compared to wild type M‐MLV. For example, in some embodiments, the increased rever se transcriptase activity at 50°C to 60°C is at least 10%, 25%, 50%, 75%, 100%, or 200 % more compared to wild type M‐MLV at an even lower reaction temperature (e.g., 37°C). L ikewise, in some embodiments, reverse transcriptases of the present invention retain at lea st 50% (e.g., 50%, 70%, 80%, 90%, etc.) reverse transcriptase activity at 50°C to 60°C for at least 5 minutes. In other embodiments, the reverse transcriptases retain at least 50% activi ty after heating to at least 50°C) for at least 5 minutes. Similarly, in other embodiments, t he reverse transcriptases as described herein retain at least 50% (e.g., 50%, 70%, 80%, 90 %, etc.) activity after heating to at least 50°C for at least 10 minutes (e.g., 10 minutes, 15 minutes, 60 minutes, etc.) at a pH ranging from about 7.3 to 8.3 when compared to wild type M ‐MLV at an even lower reaction temperature (e.g., 37°C) under similar pH conditions.
[12] In some embodiments, the reverse transcriptases of th e present invention are able to produce a cDNA that is at least 7.5 kb within 5 m inutes at a reaction temperature of about 60°C. In other embodiments, reverse transcriptases of the present invention are able to produce a cDNA that is at least 9.5 kb within 15 minutes at a reaction temperature of about 60°C.
[13] The present invention is also directed to DNA molecu les (preferably vectors)
containing a gene or nucleic acid molecule encoding the mutant reverse transcriptases of the present invention and to host cells containing such DNA molecules. Any number of hosts may be used to express the gene or nucleic acid mo lecule of interest, including prokaryotic and eukaryotic cells. Preferably, prokaryotic cells ar e used to express the polymerases of the invention. The preferred prokaryotic host according to the present invention is E. coli.
[14] The invention also provides compositions and reaction mixtures for use in reverse transcription of nucleic acid molecules, comprising on e or more mutant or modified reverse transcriptase enzymes or polypeptides as disclosed her ein. Such compositions may further comprise one or more nucleotides, a suitable buffer, and/or one or more DNA polymerases. The compositions of the invention may also comprise one or more oligonucleotide primers or
terminating agents (e.g., dideoxynucleotides). Such compositions may also comprise a stabilizing agent, such as glycerol or a surfactant. Such compositions may further comprise the use of hot start mechanisms to prevent or reduc e unwanted polymerization products during nucleic acid synthesis.
[15] The invention provides in certain embodiments, composi tions that include one or more reverse transcriptases of the invention and one or more DNA polymerases for use in amplification reactions. Such compositions may further comprise one or more nucleotides and/or a buffer suitable for amplification. The compo sitions of the invention may also comprise one or more oligonucleotide primers. Such co mpositions may also comprise a stabilizing agent, such as glycerol or a surfactant. Such compositions may further comprise the use of one or more hot start mechanisms to pre vent or reduce unwanted polymerization products during nucleic acid synthesis.
[16] The invention further provides methods for synthesis of nucleic acid molecules using one or more mutant reverse transcriptase enzymes or polypeptides as disclosed herein. In particular, the invention is directed to methods for making one or more nucleic acid molecules, comprising mixing one or more nucleic acid templates (preferably one or more RNA templates and most preferably one or more messen ger RNA templates) with one or more reverse transcriptases of the invention and incu bating the mixture under conditions sufficient to make a first nucleic acid molecule or molecules complementary to all or a portion of the one or more nucleic acid templates. In some embodiments, the first nucleic acid molecule is a single‐stranded cDNA. Nucleic ac id templates suitable for reverse transcription according to this aspect of the inventi on include any nucleic acid molecule or population of nucleic acid molecules (preferably RNA and most preferably mRNA), particularly those derived from a cell or tissue. In some embodiments, cellular sources of nucleic acid templates include, but are not limited to, bacterial cells, fungal cells, plant cells and animal cells.
[17] In certain embodiments, the invention provides methods for making one or more double‐stranded nucleic acid molecules. Such methods comprise (a) mixing one or more nucleic acid templates (preferably RNA or mRNA, and more preferably a population of mRNA templates) with one or more reverse transcriptases of the invention; (b) incubating the mixture under conditions sufficient to make a first nucleic acid molecule or molecules complementary to all or a portion of the one or mo re templates; and (c) incubating the first
nucleic acid molecule or molecules under conditions sufficient to make a second nucleic acid molecule or molecules complementary to all or a port ion of the first nucleic acid molecule or molecules, thereby forming one or more double‐strand ed nucleic acid molecules comprising the first and second nucleic acid molecules. Such me thods may include the use of one or more DNA polymerases as part of the process of maki ng the one or more double‐stranded nucleic acid molecules. The invention also concerns c ompositions useful for making such double‐stranded nucleic acid molecules. Such composit ions comprise one or more reverse transcriptases of the invention and optionally one or more DNA polymerases, a suitable buffer, one or more primers, and/or one or more nuc leotides.
[18] The invention also provides methods for amplifying a nucleic acid molecule. Such amplification methods comprise mixing the double‐stra nded nucleic acid molecule or molecules produced as described above with one or mo re DNA polymerases and incubating the mixture under conditions sufficient to amplify th e double‐stranded nucleic acid molecule. In a first preferred embodiment, the invention concer ns a method for amplifying a nucleic acid molecule, the method comprising (a) mixing one or more nucleic acid templates (preferably one or more RNA or mRNA templates and m ore preferably a population of mRNA templates) with one or more reverse transcriptases of the invention and with one or more DNA polymerases and (b) incubating the mixture under conditions sufficient to amplify nucleic acid molecules complementary to all or a por tion of the one or more templates. [19] The invention is also directed to methods for revers e transcription of one or more nucleic acid molecules comprising mixing one or more nucleic acid templates, which are preferably RNA or messenger RNA (mRNA) and more pref erably a population of mRNA molecules, with one or more reverse transcriptase of the present invention and incubating the mixture under conditions sufficient to make a nu cleic acid molecule or molecules complementary to all or a portion of the one or mo re templates. To make the nucleic acid molecule or molecules complementary to the one or mo re templates, a primer (e.g., an oligo(dT) primer) and one or more nucleotides are pr eferably used for nucleic acid synthesis in the 5 to 3 direction. Nucleic acid molecules suitable for rever se transcription according to this aspect of the invention include any nucleic acid molecule, particularly those derived from a prokaryotic or eukaryotic cell. Such cells ma y include normal cells, diseased cells, transformed cells, established cells, progenitor cells, precursor cells, fetal cells, embryonic cells, bacterial cells, yeast cells, animal cells (in cluding human cells), avian cells, plant cells
and the like, or tissue isolated from a plant or an animal (e.g., human, cow, pig, mouse, sheep, horse, monkey, canine, feline, rat, rabbit, bi rd, fish, insect, etc.). Nucleic acid molecules suitable for reverse transcription may also be isolated and/or obtained from viruses and/or virally infected cells.
[20] The invention further provides methods for amplifying or sequencing a nucleic acid molecule comprising contacting the nucleic acid molecu le with a reverse transcriptase of the present invention. In some embodiments, such methods comprise one or more polymerase chain reactions (PCRs). In some embodiments, a revers e transcription reaction is coupled to a PCR, such as in RT‐PCR.
[21] The present invention also provides kits for reverse transcription comprising the reverse transcriptase of the present invention in a packaged format. The kit for reverse transcription of the present invention can include, f or example, the reverse transcriptase, any conventional constituent necessary for reverse tra nscription such as a nucleotide primer, at least one dNTP, and a reaction buffer, and optio nally a DNA polymerase.
[22] The invention is also directed to kits for use in the methods of the invention. Such kits can be used for making, sequencing or amplifying nuc leic acid molecules (single‐ or double‐ stranded). The kits of the invention comprise a carr ier, such as a box or carton, having in close confinement therein one or more containers, suc h as vials, tubes, bottles and the like. In certain embodiments of the kits of the invention, a first container contains one or more of the reverse transcriptase enzymes of the present inve ntion. The kits of the invention may also comprise, in the same or different containers, one or more DNA polymerase (preferably thermostable DNA polymerases), one or more suitable b uffers for nucleic acid synthesis and one or more nucleotides. Alternatively, the components of the kit may be divided into separate containers (e.g., one container for each enz yme and/or component). The kits of the invention also may comprise instructions or protocols for carrying out the methods of the invention. In preferred kits of the invention, the r everse transcriptases are mutated such that the temperature at which cDNA synthesis occurs is in creased. In additional preferred kits of the invention, the enzymes (reverse transcriptases and /or DNA polymerases) in the containers are present at working concentrations.
[23] Thus, as described in detail above, in one aspect, mutant M‐MLV reverse
transcriptases are provided. Such reverse transcripta ses comprise at least one mutation at an amino acid position corresponding to the sequence for wild type M‐MLV reverse
transcriptase (SEQ ID NO:2), wherein at least one amino acid position is selected from: S67, T197, and E302. In some embodiments, the at least o ne mutation is selected from the following amino acid substitution mutations: (S67R, S67N, or S67K), (T197A, T197S, or T197G), and (E302K, E302R, or E302G). In some embo diments, the mutant reverse transcriptases further comprises at least one addition al mutation at an amino acid position selected from: P51, E69, P196, D200, H204, M289, T30 6, F309, W313, T330, L435, N454, D524, E562, D583, H594, L603, D653, and L671. In some embodiments, the at least one additional mutation is selected from the following am ino acid substitution mutations: P51L, E69K, P196S, D200N, H204R, M289L, T306K, (F309N, F309 Y, or F309I), (W313F, W313L, or W313C), T330P, (L435G, L435V, or L435R), N454K, D524G , E562Q, D583N, H594Q, L603W, (D653N or D653H), and L671P.
[24] In another aspect, mutant M‐MLV reverse transcriptas es are provided that comprise at least six mutations at an amino acid position co rresponding to the sequence for wild type M‐MLV reverse transcriptase (SEQ ID NO:2), wherein at least six amino acid positions are selected from: P51, E69, P196, D200, H204, M289, T30 6, F309, W313, T330, L435, N454, D524, E562, D583, H594, L603, D653, and L671. In some embodiments, the at least six mutations are selected from the following amino acid substitutions: P51L, E69K, P196S, D200N, H204R, M289L, T306K, (F309N, F309Y, or F309I), (W313F, W313L, or W313C), T330P, (L435G, L435V, or L435R), N454K, D524G, E562Q, D583N, H594Q, L603W, (D653N or D653H), and L671P. In some embodiments, the mutant M‐MLV reverse transcriptases further comprise at least one additional mutation at an amin o acid position selected from: S67, T197, and E302. In some embodiments, the at least one additional mutation is selected from the following amino acid substitutions: (S67R, S67N, or S67K), (T197A, T197S, or T197G), and (E302K, E302R, or E302G).
[25] In some embodiments, mutant M‐MLV reverse transcript ases are provided that have a mutation at each of the amino acid positions: P51 , S67, E69, T197, H204, E302, F309, W313, T330, L435, N454, D524, D583, H594, D653, and L671. In some embodiments, the mutant M‐MLV reverse transcriptase comprises each of the following amino acid substitution mutations: P51L, S67R, E69K, T197A, H204R, E302K, F30 9N, W313F, T330P, L435G, N454K, D524G, D583N, H594Q, D653N, and L671P.
[26] In some embodiments, the mutant M‐MLV reverse trans criptases lack RNase H activity. In yet other embodiments, the mutant M‐ MLV reverse transcriptases demonstrate
increased reverse transcriptase activity at a react ion temperature of at least 50°C compared to reverse transcriptase activity of the corresponding wild type M‐MLV reverse transcriptase. In some embodiments, the mutant M‐MLV reverse trans criptases demonstrate increased reverse transcriptase activity that is at least 10% (e.g., 10%, 25%, 50%, 75%, 80%, 90%, 100%, 200%, etc.) more than wild type M‐MLV reverse tran scriptase activity. In some
embodiments, the mutant M‐MLV reverse transcriptases possess reverse transcriptase activity after 5 minutes at 60°C that is at least 25% (e.g., 50%, 100%, 200%, etc.) of the reverse transcriptase activity of wild type M‐MLV r everse transcriptase after 5 minutes at 37°C. In some embodiments, the mutant M‐MLV reve rse transcriptases, demonstrate one or more of the following properties: increased thermostab ility; increased thermoreactivity; increased resistance to reverse transcriptase inhibitor s; increased ability to reverse transcribe difficult templates, increased speed/processi vity; and increased specificity (e.g., decreased primer‐less reverse transcription).
[27] In another aspect, mutant reverse transcriptases are provided that comprise at least 50% (e.g., 50%, 60%, 705, 80%, 90%, 95%, etc.) amin o acid sequence identity to SEQ ID NO:4. In some embodiments, the mutant reverse transcriptases comprise SEQ ID NO:4. In some embodiments, the mutant reverse transcriptases consist of SEQ ID NO:4.
[28] In some embodiments, the mutant reverse transcriptases are thermostable at temperatures between 50°C to 65°C (e.g. 50°C, 52° C, 55°C, 58°C, 60°C, and 62°C). In some embodiments, they are thermostable for at least 1 mi nute (e.g., 1 minute, 5 minutes, 15 minutes, 60 minutes, 120 minutes, etc.) at a tempera ture between 50°C to 65°C (e.g., 55°C, 60°C, etc.). In some embodiments, the mutant rever se transcriptases are thermoreactive at temperatures between 50°C to 65°C (e.g. 50°C, 52° C, 55°C, 58°C, 60°C, and 62°C). In some embodiments, the mutant reverse transcriptase are ther moreactive for at least 1 minute (e.g., 1 minute, 5 minutes, 15 minutes, 60 minutes, 120 minutes, etc.) at temperatures between 50°C to 65°C (e.g., 55°C, 60°C, etc.). In some embodiments, the mutant reverse transcriptases retain at least 10% (e.g., 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100%) reverse transcriptase activity after heating to at least 50° C (e.g., 50°C, 55°C, 60°C, 62°C, 65°C, etc.) for at least 1 minute (e.g., 1 minute, 2 minutes, 5 minutes, 10 minutes, 15 minutes, etc.). In some embodiments, the reverse transcriptases retain at least 10% (e.g., 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 1 00%) reverse transcriptase activity after heating to at least 60°C (e.g., 60°C, 62°C, 65°C, etc.) for at least 1 minute (e.g., 1
minute, 2 minutes, 5 minutes, 10 minutes, 15 minu tes, etc.). In some embodiments, the reverse transcriptases retain at least 50% (e.g., 50% , 60%, 70%, 80%, 90%, and 100%) reverse transcriptase activity after heating to at least 50° C (e.g., 50°C, 55°C, 60°C, 62°C, 65°C, etc.) fo r at least 1 minute (e.g., 1 minute, 2 minutes, 5 mi nutes, 10 minutes, 15 minutes, etc.). In some embodiments, the reverse transcriptases retain at least 10% (e.g., 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100%) reverse tra nscriptase activity after heating to at least 50°C (e.g., 50°C, 55°C, 60°C, 62°C, 65°C, ) for at least 5 minutes (e.g., 5 minutes, 10 minutes, 15 minutes, 30 minutes, etc.).
[29] In some embodiments, the mutant reverse transcriptases are mutant M‐MLV reverse transcriptases. In other embodiments, the mutant rever se transcriptases are mutant reverse transcriptases obtained from other species, including for example, fowl pox, wild boar, koala and baboon. In some embodiments, the mutant reverse transcriptases comprise regions of amino acid homology and identity, such as that depic ted by the consensus sequence listed in Figures 1A through 1D.
[30] In another aspect, compositions for nucleic acid synt hesis are provided. Such
compositions can comprise a buffer and any of the m utant reverse transcriptases described herein. In some embodiments, the compositions furthe r comprise one or more components useful for nucleic acid synthesis, such as one or m ore nucleotides, one or more DNA polymerases, one or more detergents, one or more pri mers, one or more hot start components, and/or one or more terminating agents. In some embodiments, the
termination agent is a dideoxynucleotide.
[31] In another aspect, methods for nucleic acid synthesis (such as reverse transcription and amplification) are provided. Such methods can c omprise the use of any of the mutant reverse transcriptases described herein. In some emb odiments, the methods comprise: (a) preparing a mixture comprising one or more nucleic a cid templates with one or more reverse transcriptases as described herein; and (b) incubating the mixture under conditions sufficient to make one or more first nucleic acid molecules co mplementary to all or a portion of the one or more nucleic acid templates.
[32] In other embodiments, the methods comprise: (a) mix ing one or more nucleic acid templates with one or more reverse transcriptases as described herein and one or more DNA polymerases; and (b) incubating the mixture under con ditions sufficient to amplify one or more nucleic acid molecules complementary to all or a portion of the one or more templates.
[33] In some embodiments, the nucleic acid template is a messenger RNA molecule or a population of mRNA molecules. In some embodiments, th e methods comprise a step of incubating one or more first nucleic acid molecules under conditions sufficient to make one or more second nucleic acid molecules complementary t o all or a portion of the one or more first nucleic acid molecules. In other embodiments, t he methods further comprise a step of determining the nucleotide sequence of all or a port ion of the amplified nucleic acid molecules that are complementary to all or a portion of the one or more templates. In some embodiments of the described methods, incubating is p erformed at a temperature of about 60°C.
[34] In another aspect, kits comprising mutant M‐MLV rev erse transcriptases as described herein in one or more packaged containers are provid ed.
[35] In yet another aspect, isolated nucleic acids encodin g mutant reverse transcriptases as described herein are provided.
[36] In another aspect, vectors comprising nucleic acids e ncoding mutant reverse
transcriptases as described herein are provided. In o ne embodiment, expression vectors comprising a promoter operably linked to nucleic acid s encoding mutant reverse
transcriptases as described herein are provided.
[37] In another aspect, host cells comprising nucleic acid s encoding mutant reverse transcriptases as described herein are provided. In another aspect, host cells comprising mutant reverse transcriptases or polypeptides having r everse transcriptase activity as described herein are provided.
[38] Other preferred embodiments of the present invention will be apparent to one of ordinary skill in light of the following drawings an d description of the invention, and of the claims.
BRIEF DESCRIPTION OF THE DRAWINGS [39] These and other features, aspects, and advantages of the present invention will become better understood with reference to the follow ing description and appended claims, and accompanying drawings where:
[40] FIGURES 1A through 1D show a table comprising the a mino acid sequence alignment between wild type M‐MLV reverse transcriptase (MMLV) and viral reverse transcriptases specific to other species of animals (i.e., baboon, fowl pox, koala, and wild boar). Regions of amino acid similarity and identity are seen throughou t the various RTs. A consensus sequence among the various RTs is also shown.
[41] FIGURE 2 is a fluorescent image showing RT activity of an exemplary mutant M‐MLV reverse transcriptase as disclosed herein (“Mut D9 ; SEQ ID NO:4) compared to wild type M‐ MLV reverse transcriptase (“WT MMLV”; SEQ ID NO:2 ) as well as other commercially available (“conventional”) mutant M‐MLV reverse t ranscriptases (“SSII”, “SSIII”, and “Q‐RT” ). Each lane shows the cDNA products obtained from RT reactions carried out for varying lengths of time (i.e., 5 minutes, 15 minutes or 60 minutes) and under varying reaction temperatures (i.e., 37°C, 42°C, 50°C or 60°C), as indicated. A 0.24 to 9.5 kb RNA ladder was used as the template nucleic acid for each reaction.
[42] FIGURE 3 is a fluorescent image showing RT activity of an exemplary mutant M‐MLV reverse transcriptase as disclosed herein (“Mut D9 ; SEQ ID NO:4) compared to wild type M‐ MLV reverse transcriptase (“WT MMLV” ; SEQ ID NO :2). Each lane shows the cDNA products obtained from RT reactions carried out for varying l engths of time (i.e., 10 minutes, 30 minutes or 60 minutes) either at 37°C (for WT MMLV ) or 50°C (for Mut D) and under pH 8.3 or 7.3, as indicated. A 0.5 to 10 kb RNA ladder was used as the template nucleic acid for each reaction.
[43] FIGURE 4 is a fluorescent image showing RT activity of an exemplary mutant M‐MLV reverse transcriptase as disclosed herein (“Mut D9 ; SEQ ID NO:4) compared to wild type M‐ MLV reverse transcriptase (“WT MMLV” ; SEQ ID NO :2) as well as other commercially available (“conventional”) mutant M‐MLV reverse t ranscriptases (“SSIII” and “C‐RT”). Each lane shows the cDNA products obtained from RT reacti ons carried out for varying lengths of time (i.e., 5 minutes, 10 minutes, 30 minutes or 60 minutes) at 60°C and at pH 8.3. A 0.5 to 10 kb RNA ladder was used as the template nucleic acid for each reaction.
[44] FIGURE 5 is a photograph of an ethidium bromide sta ined gel showing RT activity of an exemplary mutant M‐MLV reverse transcriptase as disclosed herein (“Mut D9”; SEQ ID NO:4) compared to other commercially available mutant M‐MLV reverse transcriptases (“SSIII” and “M‐RT”). Each lane shows the products (amplified via PCR) obtained from RT reactions carried out using different primers: (1) no primer; (2) oligo(dT) 20 primer; (3) oligo(dT) 20 LNA primer; or (4) PolE 2.5Rve gene‐specific primer and under varying reaction conditions (i.e., “NON‐HS‐RT‐rxn” or “HS‐R T‐rxn”; HS= hot start), as indicated and as described in more detail in Example 4. A different amount (i.e., 10 ng, 50 ng, or 100 ng) of a 1 kb target (“Hela RNA”) was used as the template nucleic acid for each reaction.
[45] FIGURE 6 is a fluorescent image showing RT activity of an exemplary mutant reverse transcriptase as disclosed herein (“Mut D9”; SEQ ID NO:4) compared to wild type M‐MLV reverse transcriptase (“WT MMLV”; SEQ ID NO:2) as well as other commercially available (“conventional”) mutant M‐MLV reverse transcriptas es (“SSIII” and “C‐RT”). Each lane shows the cDNA products obtained from RT reactions carried out for 60 minutes at 50°C and in the presence of various inhibitors at various concentratio ns, as indicated. A 0.5 to 10 kb RNA ladder was used as the template nucleic acid for ea ch reaction.
[46] FIGURE 7 illustrates the RT activity in graphical fo rmat of the different RTs in the presence of inhibitors, as shown in Figure 6. RT activity was normalized to reactions comprising no inhibitor (indicated as 100% activity). Dark shading represents the lowest RT activity, while light shading represents the highest RT activity (Black to White = Lowest to Highest Activity).
[47] FIGURES 8A and 8B list the nucleic acid sequence fo r wild type M‐MLV reverse transcriptase (SEQ ID NO:1)
[48] FIGURE 9 lists the amino acid sequence for wild typ e M‐MLV reverse transcriptase (SEQ ID NO:2)
[49] FIGURES 10A and 10B list the nucleic acid sequence for an exemplary mutant (“Mut D9”) M‐MLV reverse transcriptase (SEQ ID NO:3) of the invention.
[50] FIGURE 11 lists the amino acid sequence for an exem plary mutant (“Mut D9”) M‐MLV reverse transcriptase (SEQ ID NO:4) of the invention.
DETAILED DESCRIPTION [51] Provided herein are reverse transcriptases that have been mutated to increase thermostability and/or thermoreactivity, reverse transcr iptase inhibitor resistance, cDNA generation with difficult RNA templates, and specifici ty. In certain embodiments, the invention provides methods of making such reverse tra nscriptases by mutating or modifying specific amino acids of the corresponding wild type reverse transcriptases. In other embodiments, the invention provides methods of produci ng, amplifying and/or sequencing nucleic acid molecules, in illustrative embodiments, c DNA molecules, using compositions and/or reactions mixtures containing such mutant rever se transcriptase enzymes. For example, the reverse transcriptases of the invention are well‐suited for nucleic acid synthesis methods including, but not limited to, RNA sequencing and reverse transcription of crude samples, difficult RNA templates and gene specific se quences. Definitions
[52] In the description that follows, a number of terms are used that have the following meaning:
[53] Operably linked. As used herein “operably linked” means that a nucleic acid element is positioned so as to influence the initiation of expression of the polypeptide encoded by the structural gene or other nucleic acid molecule.
[54] Substantially Pure. As used herein “substantially pu re” means that the desired material is essentially free from contaminating cellul ar components which are associated with the desired material in nature. In a preferred aspect, a reverse transcriptase of the invention has 25% or less, preferably 15% or less, more preferably 10% or less, more preferably 5% or less, and still more preferably 1% or less contaminating cellular
components. In another aspect, the reverse transcripta ses of the invention have no detectable protein contaminants when 200 units of rev erse transcriptase are run on a protein gel (e.g., SDS‐PAGE) and stained with Cooma ssie blue. Contaminating cellular components may include, but are not limited to, enzy matic activities such as phosphatases, exonucleases, endonucleases or undesirable DNA polymera se enzymes. Preferably, reverse transcriptases of the invention are substantially pure .
[55] Substantially isolated. As used herein “substantially isolated” means that the
polypeptide of the invention is essentially free from contaminating proteins, which may be
associated with the polypeptide of the invention i n nature and/or in a recombinant host. In one aspect, a substantially isolated reverse transcrip tase of the invention has 25% or less, preferably 15% or less, more preferably 10% or less, more preferably 5% or less, and still more preferably 1% or less contaminating proteins. In another aspect, in a sample of a substantially isolated polypeptide of the invention, 7 5% or greater (preferably 80%, 85%, 90%, 95%, 98%, or 99% or greater) of the protein i n the sample is the desired reverse transcriptase of the invention. The percentage of con taminating protein and/or protein of interest in a sample may be determined using techniq ues known in the art, for example, by using a protein gel (e.g., SDS‐PAGE) and staining the gel with a protein dye (e.g., Coomassie blue, silver stain, amido black, etc.). In another a spect, the reverse transcriptases of the invention have no detectable protein contaminants when 200 units of reverse transcriptase are run on a protein gel (e.g., SDS‐PAGE) and sta ined with Coomassie blue.
[56] Terminating agent. The term “terminating agent” which is sometimes used
interchangeably with “terminator base” refers to a nucleotide which is incapable of being extended by a DNA or RNA polymerase. Such nucleoti des can include, for example, dideoxynucleotides (ddNTPs) or various sugar‐modified nucleotides.
[57] Reverse Transcriptase. As used herein, the term “ reverse transcriptase” refers to a protein, polypeptide, or polypeptide fragment that exh ibits reverse transcriptase activity. [58] Reverse Transcriptase Activity. As used herein, the term "reverse transcriptase activity," “reverse transcription activity,” or "re verse transcription" indicates the capability of an enzyme to synthesize DNA strand (that is, complem entary DNA or cDNA) using RNA as a template.
[59] Mutation. As used herein, the term "mutation" or mutant” indicates a change or changes introduced in a wild type DNA sequence or a wild type amino acid sequence. Examples of mutations include, but are not limited t o, substitutions, insertions, deletions, and point mutations. Mutations can be made either at the nucleic acid level or at the amino acid level.
[60] Thermostable. For the purposes of this disclosure, thermostable” generally refers to an enzyme, such as a reverse transcriptase (“thermo stable reverse transcriptase”), which retains a greater percentage or amount of its activi ty after a heat treatment than is retained by the same enzyme having wild type thermostability, after an identical treatment. Thus, a reverse transcriptase having increased/enhanced thermost ability may be defined as a
reverse transcriptase having any increase in thermo stability, preferably from about 1.2 to about 10,000 fold, from about 1.5 to about 10,000 f old, from about 2 to about 5,000 fold, or from about 2 to about 2000 fold (preferably greater than about 5 fold, more preferably greater than about 10 fold, still more preferably gr eater than about 50 fold, still more preferably greater than about 100 fold, still more p referably greater than about 500 fold, and most preferably greater than about 1000 fold) retenti on of activity after a heat treatment sufficient to cause a reduction in the activity of a reverse transcriptase that is wild type for thermostability. Preferably, the mutant reverse transcr iptase of the invention is compared to the corresponding un‐mutated or wild type reverse t ranscriptase to determine the relative enhancement or increase in thermostability. For exampl e, after a heat treatment at 60°C for 5 minutes, a thermostable reverse transcriptase may r etain approximately 90% of the activity present before the heat treatment, whereas a reverse transcriptase that is wild type for thermostability may retain 10% of its original activi ty. Likewise, after a heat treatment at 60°C for 15 minutes, a thermostable reverse transcri ptase may retain approximately 80% of its original activity, whereas a reverse transcriptase that is wild type for thermostability may have no measurable activity. Similarly, after a heat treatment at 60°C for 15 minutes, a thermostable reverse transcriptase may retain approxima tely 50%, approximately 55%, approximately 60%, approximately 65%, approximately 70% , approximately 75%,
approximately 80%, approximately 85%, approximately 90% , or approximately 95% of its original activity, whereas a reverse transcriptase tha t is wild type for thermostability may have no measurable activity or may retain 20%, 15%, 10%, or none of its original activity. In the first instance (i.e., after heat treatment at 60 °Cfor 5 minutes), the thermostable reverse transcriptase would be said to be 9‐fold more ther mostable than the wild type reverse transcriptase (90% compared to 10%). Examples of cond itions which may be used to measure thermostability of an enzyme such as reverse transcriptases are set out in further detail below and in the Examples.
[61] The thermostability of a reverse transcriptase can be determined, for example, by comparing the residual activity of a reverse transcri ptase that has been subjected to a heat treatment, e.g., incubated at 60°C for a given peri od of time, for example, five minutes, to a control sample of the same reverse transcriptase that has been incubated at room temperature for the same length of time as the heat treatment. Typically the residual activity may be measured by following the incorporation of a radiolabled deoxyribonucleotide into
an oligodeoxyribonucleotide primer using a complemen tary oligoribonucleotide template. For example, the ability of the reverse transcriptase to incorporate [α‐ 32 P]‐dGTP into an oligo‐dG primer using a poly(riboC) template may be assayed to determine the residual activity of the reverse transcriptase. Other methods for measuring residual activity are known by those of skill in the art, such as by in corporation of unlabeled nucleotides into a fluorescently‐labeled primer. See, for example, Nik iforov, T. T., Anal Biochem., 2011, 412(2): 229‐36, which is hereby incorporated by reference.
[62] In another aspect, thermostable reverse transcriptases of the invention may include any reverse transcriptase which is inactivated at a higher temperature compared to the corresponding wild type, un‐mutated reverse transcrip tase. Preferably, the inactivation temperature for the thermostable reverse transcriptases of the invention is from about 2°C to about 50°C (e.g., about 2°C, about 4°C, about 6°C, about 8°C, about 10°C, about 12°C, about 14°C, about 16°C, about 18°C, about 19°C, about 20°C, about 21°C, about 22°C, about 23°C, about 24° C, about 26°C, about 28°C, about 30°C, about 32°C, about 34°C, about 36°C, about 38°C, about 40°C, about 42°C, about 44°C, about 46°C, about 48°C, or about 50°C) higher than the inactivation temperature for the corr esponding wild type, un‐mutated reverse transcriptase. More preferably, the inactivatio n temperature for the reverse transcriptases of the invention is from about 5°C t o about 50°C, from about 5°C to about 40°C, from about 5°C to about 30°C, or from abou t 5°C to about 25°C greater than the inactivation temperature for the corresponding wild ty pe, un‐mutated reverse transcriptase, when compared under the same conditions. In some emb odiments, mutant reverse transcriptases of the invention possess reverse transc riptase activity after at least one minute (e.g., 1 minute, 2 minutes, 5 minutes, 10 mi nutes, 15 minutes, 30 minutes, etc.) at an elevated temperature (e.g., 50°C, 55°C, 60°C, 65°C ) that is at least 10% (e.g., 10%, 25%, 50%, 75%, 100%, 150%, 200%, 300%, etc.) of the reverse t ranscriptase activity of wild type reverse transcriptase after 5 minutes at a lower temperature (e.g., 50°C, 45°C, 42°C, 40°C, 37°C). [63] The difference in inactivation temperature for the re verse transcriptase of the invention compared to its corresponding wild type, un ‐mutated reverse transcriptase can be determined by treating samples of such reverse transc riptases at different temperatures for a defined time period and then measuring residual re verse transcriptase activity, if any, after the samples have been heat treated. Determination of the difference or delta in the inactivation temperature between the test reverse tran scriptase compared to the wild type,
un‐mutated control is determined by comparing the difference in temperature at which each reverse transcriptase is inactivated (i.e., no residua l reverse transcriptase activity is measurable in the particular assay used). As will be recognized, any number of reverse transcriptase assays may be used to determine the di fferent or delta of inactivation temperatures for any reverse transcriptases tested.
[64] In another aspect, thermostability of a reverse trans criptase of the invention is determined by measuring the half‐life of the revers e transcriptase activity of a reverse transcriptase of interest. Such half‐life may be co mpared to a control or wild type reverse transcriptase to determine the difference (or delta) in half‐life. Half‐life of the reverse transcriptases of the invention are preferably determi ned at elevated temperatures (e.g., greater than 37° C) and preferably at temperatures ranging from 40° C to 80° C, more preferably at temperatures ranging from 45° C to 75 ° C, 50° C to 70° C, 55° C to 65° C, and 5 8° C to 62° C. Preferred half‐lives of the reverse transcriptases of the invention may range from 4 minutes to 10 hours, 4 minutes to 7.5 hours, 4 minutes to 5 hours, 4 minutes to 2.5 hours, or 4 minutes to 2 hours, depending upon the tempera ture used. For example, the reverse transcriptase activity of the reverse transcriptases o f the invention may have a half‐life of at least 4 minutes, at least 5 minutes, at least 6 mi nutes, at least 7 minutes, at least 8 minutes, at least 9 minutes, at least 10 minutes, at least 11 minutes, at least 12 minutes, at least 13 minutes, at least 14 minutes, at least 15 minutes, at least 20 minute, at least 25 minutes, at least 30 minutes, at least 40 minutes, at least 50 minutes, at least 60 minutes, at least 70 minutes, at least 80 minutes, at least 90 minutes, at least 100 minutes, at least 115 minutes, at least 125 minutes, at least 150 minutes, at leas t 175 minutes, at least 200 minutes, at least 225 minutes, at least 250 minutes, at least 275 min utes, at least 300 minutes, at least 400 minutes, at least 500 minutes at temperatures of 48 C, 50° C, 52° C, 54° C, 56° C, 58° C, 60 C, 62° C, 64° C, 66° C, 68° C, and/or 70° C.
[65] Thermoreactivity. As used herein, “thermoreactivity or “thermoreactive” refers to the ability of a reverse transcriptase to exhibit en zyme activity at elevated temperatures. [66] Thermostability. As used herein, “thermostability” or “thermostable” refers to the ability to withstand exposure to elevated temperatures , but not necessarily show activity at such elevated temperatures.
[67] Processivity. As used herein, “processivity” refe rs to the ability of a reverse
transcriptase to continuously extend a primer without disassociating from the nucleic acid
template. The length of a template an enzyme is capable of replicating (e.g., “X enzyme can polymerase a 9 kb template” or “X enzyme can pr oduce a cDNA that is about 6000 bases in length.”) can also be used to describe the process ivity of a given enzyme.
[68] Inhibitor resistance. As used herein, “inhibitor r esistance” refers to the ability of a reverse transcriptase to perform reverse transcription in the presence of a compound, chemical, protein, buffer, etc. that is typically inh ibitory to the reverse transcriptase
(prevents or inhibits reverse transcriptase activity).
[69] Fidelity. Fidelity refers to the accuracy of polymeri zation, or the ability of the reverse transcriptase to discriminate correct from incorrect s ubstrates, (e.g., nucleotides) when synthesizing nucleic acid molecules which are compleme ntary to a template. The higher the fidelity of a reverse transcriptase, the less the re verse transcriptase misincorporates nucleotides in the growing strand during nucleic acid synthesis; that is, an increase or enhancement in fidelity results in a more faithful r everse transcriptase having decreased error rate or decreased misincorporation rate.
[70] About. The term “about” as used herein, means th e recited number plus or minus 10%. Thus, “about 100” includes the full range o f values within the range of 90 through 110.
Sources of Reverse Transcriptases
[71] In accordance with the invention, mutations or modifi cations may be made in any reverse transcriptase or polypeptide having reverse tr anscriptase activity in order to increase the thermostability and/or thermoreactivity of the enz yme, or confer other properties upon the enzyme, such as increased specificity, increased resistance to reverse transcriptase inhibitors, and/or increased ability to generate cDNAs from difficult RNA templates.
[72] Reverse transcriptases for use in the compositions, m ethods and kits of the invention include any enzyme or polypeptide having reverse tran scriptase activity. Such enzymes include, but are not limited to, retroviral reverse transcriptase, retrotransposon reverse transcriptase, hepatitis B reverse transcriptase, cauli flower mosaic virus reverse
transcriptase, bacterial reverse transcriptase, Tth DNA polymerase, Taq DNA polymerase (Saiki, R. K., et al., Science 239:487‐491 (1988); U.S. Pat. Nos. 4,889,818 and 4,965,188), Tne DNA polymerase (WO 96/10640), Tma DNA polymerase (U.S . Pat. No. 5,374,553) and mutants, fragments, variants or derivatives thereof (s ee, e.g., commonly owned U.S. Pat.
Nos. 5,948,614 and 6,015,668, which are incorporate d by reference herein in their entireties).
[73] Preferred reverse transcriptases include retroviral rev erse transcriptases such as Maloney Murine Leukemia Virus (M‐MLV) reverse transc riptase, Human Immunodeficiency Virus (HIV) reverse transcriptase, Rous sarcoma virus (RSV) reverse transcriptase, Avian Myeloblastosis Virus (AMV) reverse transcriptase, Rous associated virus (RAV) reverse transcriptase, and Myeloblastosis Associated Virus (MAV ) reverse transcriptase or other Avian sarcoma leukosis virus (ASLV) reverse transcript ases. Additional reverse transcriptases which may be mutated to make the reverse transcripta ses of the invention include bacterial reverse transcriptases (e.g., Escherichia coli reverse transcriptase) (see, e.g., Mao et al., Biochem. Biophys. Res. Commun. 227:489‐93 (1996)) an d reverse transcriptases of
Saccharomyces cerevisiae (e.g., reverse transcriptases of the Ty1 or Ty3 retrotransposons) (see, e.g., Cristofari et al., Jour. Biol. Chem. 274 :36643‐36648 (1999); Mules et al., Jour. Virol. 72:6490‐6503 (1998)). Other reverse transcriptases that can be used in accordance with the described invention include, but are not limited to reverse transcriptases isolated from viruses isolated from, for example, baboon, fowl pox, koala bear, and wild boar species. [74] The present invention further provides polynucleotides which are identical or have the same functions as the reverse transcriptases incl uded in the present invention. The phrase "identical” or “have same functions as" he rein indicates that two polynucleotides demonstrate at least 70%, preferably at least 80%, m ore preferably at least 90%, and most preferably at least 95% amino acid identity when the y are properly arranged by a well‐ informed computerized algorithm.
[75] The invention further includes reverse transcriptases which are 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99 % identical at the amino acid level to a wild type reverse transcriptase (e.g., M‐MLV reverse transcriptase enzyme; SEQ ID NO:2), AMV reverse transcriptase, RSV reverse transcriptase, HIV reverse transcriptase, etc.) and exhibit increased thermostability and/or other desired properties of the invention. Also included within the invention are reverse transcriptas es which are 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical at the amino acid level to a reverse transcriptase comprising the amino acid sequence set out below in SEQ ID NO:4 and exhibit increased thermostability and/or thermoreactivity.
[76] The invention also includes fragments of reverse tran scriptases which comprise at least 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, or 700 amino acid residues and retain one or more activities associated with reverse transc riptases. Such fragments may be obtained by deletion mutation, by recombinant techniqu es that are routine and well‐known in the art, or by enzymatic digestion of the revers e transcriptase(s) of interest using any of a number of well‐known proteolytic enzymes. Reverse tr anscriptase fragments of the invention further comprise polypeptides which are 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to one or more of the fragments set out above. The invention also concerns various combinations of any number of these fragments.
[77] By a protein or protein fragment having an amino ac id sequence at least, for example, 70% “identical” to a reference amino acid sequenc e it is intended that the amino acid sequence of the protein is identical to the referenc e sequence except that the protein sequence may include up to 30 amino acid alterations per each 100 amino acids of the amino acid sequence of the reference protein. In other wor ds, to obtain a protein having an amino acid sequence at least 70% identical to a reference amino acid sequence, up to 30% of the amino acid residues in the reference sequence may be deleted or substituted with another amino acid, or a number of amino acids up to 30% of the total amino acid residues in the reference sequence may be inserted into the reference sequence. These alterations of the reference sequence may occur at the amino (N‐) and /or carboxy (C‐) terminal positions of the reference amino acid sequence and/or anywhere bet ween those terminal positions, interspersed either individually among residues in the reference sequence and/or in one or more contiguous groups within the reference sequence. As a practical matter, whether a given amino acid sequence is, for example, at least 70% identical to the amino acid sequence of a reference protein can be determined conventional ly using known computer programs such as those described above for nucleic acid seque nce identity determinations, or using the CLUSTAL W program (Thompson, J. D., et al., Nucleic Acids Res. 22:4673‐4680 (1994)).
[78] Sequence identity may be determined by comparing a r eference sequence or a subsequence of the reference sequence to a test sequ ence. The reference sequence and the test sequence are optimally aligned over an arbitrary number of residues termed a comparison window. In order to obtain optimal alignme nt, additions or deletions, such as gaps, may be introduced into the test sequence. The percent sequence identity is
determined by determining the number of positions at which the same residue is present in
both sequences and dividing the number of matching positions by the total length of the sequences in the comparison window and multiplying by 100 to give the percentage. In addition to the number of matching positions, the nu mber and size of gaps is also considered in calculating the percentage sequence identity.
[79] Sequence identity is typically determined using comput er programs. A representative program is the BLAST (Basic Local Alignment Search T ool) program publicly accessible at the National Center for Biotechnology Information (NCBI, h ttp://www.ncbi.nlm.nih.gov/). This program compares segments in a test sequence to sequ ences in a database to determine the statistical significance of the matches, then identifi es and reports only those matches that that are more significant than a threshold level. A suitable version of the BLAST program is one that allows gaps, for example, version 2.X (Alts chul, et al., Nucleic Acids Res.
25(17):3389‐402, 1997). Standard BLAST programs for searching nucleotide sequences (blastn) or protein (blastp) may be used. Translated query searches in which the query sequence is translated, i.e., from nucleotide sequence to protein (blastx) or from protein to nucleic acid sequence (tbblastn) may also be used as well as queries in which a nucleotide query sequence is translated into protein sequences i n all 6 reading frames and then compared to an NCBI nucleotide database which has be en translated in all six reading frames (tbblastx).
[80] Additional suitable programs for identifying proteins with sequence identity or similarity to the proteins of the invention include, but are not limited to, PHI‐BLAST (Pattern Hit Initiated BLAST, Zhang, et al., Nucleic Acids Re s. 26(17):3986‐90, 1998) and PSI‐BLAST (Position‐Specific Iterated BLAST, Altschul, et al., Nucleic Acids Res. 25(17):3389‐402, 1997). [81] Programs may be used with default searching parameter s. Alternatively, one or more search parameter may be adjusted. Selecting suitable search parameter values is within the abilities of one of ordinary skill in the art.
[82] Some reverse transcriptase enzymes for use in the in vention include those that are reduced, substantially reduced, or lacking in RNase H activity. Such enzymes that are reduced or substantially reduced in RNase H activity include RNase H− derivatives of any of the reverse transcriptases described above and may be obt ained by mutating, for example, the RNase H domain within the reverse transcriptase of i nterest, for example, by introducing one or more (e.g., one, two, three, four, five, ten, tw elve, fifteen, twenty, thirty, etc.) point mutations, one or more (e.g., one, two, three, four, five, ten, twelve, fifteen, twenty, thirty,
etc.) deletion mutations, and/or one or more (e.g. , one, two, three, four, five, ten, twelve, fifteen, twenty, thirty, etc.) insertion mutations as described elsewhere herein. For example, such mutations are described in U.S. Patent Nos. 8,5 41,219 and 8,753,845, and are herein incorporated by reference in their entirety.
[83] By an enzyme “substantially reduced in RNase H act ivity” is meant that the enzyme has less than about 30%, less than about 25%, less than about 20%, more preferably less than about 15%, less than about 10%, less than abou t 7.5%, or less than about 5%, and most preferably less than about 5% or less than about 2% , of the RNase H activity of the corresponding wild type or RNase H+ enzyme, such as wild type Maloney Murine Leukemia Virus (M‐MLV), Avian Myeloblastosis Virus (AMV) or Rous Sarcoma Virus (RSV) reverse transcriptases. A reduction in RNase H activity means any reduction in the activity compared, for example, to the corresponding wild type or un‐ mutated reverse transcriptase. Thus, in one aspect, the reverse transcriptase of the inventio n can have 50%, 40%, 30%, 20%, 10%, 5%, 1% or no RNase H activity compared to the corr esponding wild type reverse
transcriptase.
[84] Reverse transcriptases having reduced, substantially re duced, undetectable or lacking RNase H activity have been previously described (see U.S. Pat. No. 5,668,005, U.S. Pat. No. 6,063,608, and PCT Publication No. WO 98/47912). The RNase H activity of any enzyme may be determined by a variety of assays, such as those described, for example, in U.S. Pat. No. 5,244,797, in Kotewicz, M. L., et al., Nucl. Acids Res. 16:265 (1988), in Gerard, G. F., et al., FOCUS 14(5):91 (1992), in PCT publication number WO 98/47912, and in U.S. Pat. No. 5,668,005, the disclosures of all of which are fully incorporated herein by reference.
[85] Reverse transcriptases having no detectable RNase H a ctivity or lacking RNase H activity by one or more of the described assays are also contemplated in accordance with the invention. Thus, in some embodiments, mutated enzymes for use in the invention include, but are not limited to, M‐MLV H− reverse transcr iptase, RSV H− reverse transcriptase, AMV H− reverse transcriptase, RAV H− reverse transcrip tase, MAV H− reverse transcriptase and HIV H− reverse transcriptase. It will be understood by one of ordinary skill, however, that any enzyme capable of producing a DNA molecule from a r ibonucleic acid molecule (i.e., having reverse transcriptase activity) that is reduced or su bstantially reduced in RNase H activity may be equivalently used in accordance with the inve ntion.
[86] Alternatively, reverse transcriptase enzymes of the in vention may not contain any modification or mutation in the RNase H domain which reduces RNase H activity. Thus, in other embodiments, the reverse transcriptases of the invention can have 100% RNase H activity which is equivalent to the corresponding wil d type reverse transcriptase.
[87] Reverse transcriptase enzymes or polynucleotides for u se in the invention also include those in which terminal deoxynucleotidyl trans ferase (TdT) activity has been reduced, substantially reduced, or eliminated. Such enzymes tha t are reduced or substantially reduced in terminal deoxynucleotidyl transferase activity, or in which TdT activity has been eliminated, may be obtained by mutating, for example, amino acid residues within the reverse transcriptase of interest which are in close proximity or in contact with the template‐ primer, for example, by introducing one or more (e.g ., one, two, three, four, five, ten, twelve, fifteen, twenty, thirty, etc.) point mutations, one o r more deletion mutations, and/or one or more insertion mutations. Reverse transcriptases which exhibit decreased TdT activity are described in U.S. Patent No. 7,056,716, issued June 6, 2006 (the entire disclosure of which is incorporated herein by reference).
[88] Enzymes for use in the invention also include those that exhibit increased fidelity. Reverse transcriptases which exhibit increased fidelity are described in U.S. Appl. No. 60/189,454, filed Mar. 15, 2000, and U.S. Patent No. 7,056,716, issued June 6, 2006 (the entire disclosures of which are incorporated herein b y reference).
[89] Thus, in specific embodiments, the invention includes reverse transcriptases which exhibit increased thermostability and/or increased ther moreactivity and, optionally, also exhibit one or more of the following characteristics: (1) reduced or substantially reduced RNase H activity, (2) reduced or substantially reduce d TdT activity, and/or (3) increased fidelity.
[90] The present invention further provides nucleic acid m olecules which encode the above described mutant reverse transcriptases and reve rse transcriptase fragments. In some embodiments, the nucleic acid molecules encoding the mutant reverse transcriptases and reverse transcriptase fragments are at least 80% (e.g ., 80%, 85%, 90%, 95%, 99%) identical to SEQ ID NO:3. In some embodiments, the nucleic acid molecules encoding the mutant reverse transcriptases and reverse transcriptase fragme nts comprise SEQ ID NO:3.
[91] As will be understood by one of ordinary skill in the art, mutated reverse
transcriptases in accordance with the invention may b e obtained by recombinant or genetic
engineering techniques that are routine and well‐ known in the art (see, e.g., Kotewicz, M. L., et al., Nucl. Acids Res. 16:265 (1988); Soltis, D. A., and Skalka, A. M., Proc. Natl. Acad. Sci. USA 85:3372‐3376 (1988)); U.S. Pat. No. 5,668,005; and PCT publication no. WO 98/47912. Mutant reverse transcriptases can, for example, be ob tained by mutating the gene(s) or nucleic acid sequences encoding the reverse transcript ase or polynucleotide having reverse transcriptase activity, such as those described above, by site‐directed or random
mutagenesis. Such mutations may include point mutation s, deletion mutations and insertional mutations. Preferably, one or more point mutations (e.g., substitution of one or more amino acids with one or more different amino a cids) are used to construct mutant reverse transcriptases of the invention. Fragments of reverse transcriptases may be obtained by deletion mutation by recombinant techniques that a re routine and well‐known in the art, or by enzymatic digestion of the reverse transcriptas e(s) of interest using any of a number of well‐known proteolytic enzymes.
[92] To clone a gene or other nucleic acid molecule enco ding a reverse transcriptase which will be mutated in accordance with the invention, is olated, DNA which contains the reverse transcriptase gene or open reading frame may be used to construct a recombinant DNA library. Any vector, well known in the art, can be used to clone the reverse transcriptase of interest. However, the vector used must be compatible with the host in which the recombinant vector will be transformed.
[93] The present invention also provides transformants tran sformed by the expression vector. The transformant of the present invention c an be easily constructed by inserting the said expression vector into random prokaryotic cells or eukaryotic cells. The method to introduce a specific vector into cells is well‐know n to those in the art. In a preferred embodiment of the present invention, a pBAD vector c omprising the mutant gene or polynucleotide of the present invention (+/‐ an add itional unrelated sequence, such as a His Tag) is introduced in E. coli Top10 cells, leading to the construction of a transformant.
[94] The present invention also provides an expression vec tor containing the genes or polynucleotides of the present invention. The vector used for the construction of the expression vector of the present invention is not li mited, and any conventional vector for the transformation of prokaryotes or eukaryotes can be us ed. In some embodiments of the present invention, recombinant expression vectors are constructed by inserting a mutant gene represented by SEQ. ID. NO: 3.
[95] Prokaryotic vectors for constructing the plasmid libra ry include plasmids such as those capable of replication in E. coli such as, fo r example, pBR322, ColE1, pSC101, pUC‐ vectors (pUC18, pUC19, etc.: In: Molecular Cloning, A Laboratory Manual, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. (1982); an d Sambrook et al., In: Molecular Cloning A Laboratory Manual (2d ed.) Cold Spring Harbor Labo ratory Press, Cold Spring Harbor, N.Y. (1989)). Bacillus plasmids include pC194, pUB110, pE19 4, pC221, pC217, etc. Such plasmids are disclosed by Glyczan, T. In: The Molecular Biolo gy Bacilli, Academic Press, York (1982), 307‐329. Suitable Streptomyces plasmids include pIJ10 1 (Kendall et al., J. Bacteriol.
169:4177‐4183 (1987)). Pseudomonas plasmids are revie wed by John et al., (Rad. Insec. Dis. 8:693‐704 (1986)), and Igaki, (Jpn. J. Bacteriol. 3 3:729‐742 (1978)). Broad‐host range plasmids or cosmids, such as pCP13 (Darzins and Chak rabarty, J. Bacteriol. 159:9‐18 (1984)) can also be used for the present invention. Preferre d vectors for cloning the genes and nucleic acid molecules of the present invention are prokaryotic vectors. Preferably, pBAD, pCP13 and pUC vectors are used to clone the genes of the present invention. Other suitable vectors are known to those skilled in the art and are commercially available.
[96] Suitable hosts for cloning the reverse transcriptase genes and nucleic acid molecules of interest are prokaryotic hosts. One example of a prokaryotic host is E. coli. However, the desired reverse transcriptase genes and nucleic acid molecules of the present invention may be cloned in other prokaryotic hosts including, but not limited to, hosts in the genera Escherichia, Bacillus, Streptomyces, Pseudomonas, Salmon ella, Serratia, and Proteus. Bacterial hosts of particular interest include E. col i DH10B, which may be obtained from Life Technologies, Corp. (Carlsbad, Calif.).
[97] Eukaryotic hosts for cloning and expression of the r everse transcriptase of interest include yeast, fungal, and mammalian cells. Expression of the desired reverse transcriptase in such eukaryotic cells may require the use of eukaryo tic regulatory regions which include eukaryotic promoters. Cloning and expressing the rever se transcriptase gene or nucleic acid molecule in eukaryotic cells may be accomplished by well‐known techniques using well known eukaryotic vector systems.
[98] Once a DNA library has been constructed in a partic ular vector, an appropriate host is transformed by well‐known techniques. In some embodi ments, transformed cells are plated at a density to produce approximately 200‐300 trans formed colonies per petri dish. For selection of reverse transcriptase, colonies can then be screened for the expression of a
reverse transcriptase or a thermostable reverse tra nscriptase using methods well‐known to those skilled in the art. For example, in some embo diments, overnight cultures of individual transformant colonies are lysed, heated at 50°C for 15 minutes and assayed for reverse transcriptase or thermostable reverse transcriptase act ivity and/or other desirable activities using a fluorescently‐labeled stem loop template (e. g. FRET assay). See, for example, Nikiforov, T. T., Anal Biochem., 2011, 412(2): 229‐ 36. In some embodiments, thermostable reverse transcriptase activity and/or other desirable activity are detected, the mutant is sequenced to determine which amino acids maintain rev erse transcriptase activity. The gene or nucleic acid molecule encoding a reverse transcrip tase of the present invention can be cloned using techniques known to those in the art.
Mutant Reverse Transcriptases
[99] In accordance with the invention, a number of specif ied mutations can be made to the reverse transcriptases and, in a preferred aspect , multiple mutations can be made to result in an increased thermostability, thermoactivity, increased resistance to inhibitors, and/or to confer other desired properties on reverse transcriptases as described. Such mutations include point mutations, frame shift mutatio ns, deletions and insertions.
Preferably, one or more point mutations, resulting in one or more amino acid substitutions, are used to produce reverse transcriptases having enh anced or increased thermostability and/or thermoreactivity or increased resistance to inh ibitors.
[100] Mutations can be introduced into reverse transcriptase s of the present invention using any methodology known to those of skill in th e art. Mutations can be introduced randomly by, for example, conducting a PCR reaction in the presence of manganese as a divalent metal ion cofactor. Alternatively, oligonucleo tide directed mutagenesis may be used to create the mutant polymerases which allows for al l possible classes of base pair changes at any determined site along the encoding DNA molecu le. In general, this technique involves annealing an oligonucleotide complementary (except for one or more mismatches) to a single stranded nucleotide sequence coding for the re verse transcriptase of interest. The mismatched oligonucleotide is then extended by DNA po lymerase, generating a double‐ stranded DNA molecule which contains the desired chan ge in sequence in one strand. The changes in sequence can, for example, result in the deletion, substitution, or insertion of an
amino acid. The double‐stranded polynucleotide can then be inserted into an appropriate expression vector, and a mutant polypeptide can thus be produced. The above‐described oligonucleotide directed mutagenesis can, for example, be carried out via PCR.
[101] In general, the invention provides, in part, reverse transcriptases with one or more (e.g., one, two, three, four, five, ten, twelve, fif teen, eighteen, twenty, etc.) mutations or modification at specified amino acid sites which rend er the reverse transcriptase more thermostable and/or thermoreactive compared to its un mutated counterpart. The invention also provides reverse transcriptases with one or more specified mutations or modification which render the reverse transcriptase more efficient (e.g., having increased speed and/or processivity), more specific, more resistant to revers e transcriptase inhibitors than a corresponding un‐mutated reverse transcriptase, and/or better able to generate cDNAs from difficult RNA templates.
[102] In some embodiments, the mutations or modifications o f the reverse transcriptases provided by the invention are made in a recognized region of the reverse transcriptase enzyme (e.g., pol or RNase H region) in such a way as to produce a mutated reverse transcriptase having increased or enhanced thermostabil ity and/or thermoreactivity. Modifications or mutations may also be made in other regions in accordance with the invention (e.g., such as those regions know to play a role in enzyme Kd, thermostability, fidelity, substrate binding, etc.). Thus, the inventio n includes reverse transcriptases which exhibit increased thermostability (as well as other p roperties), as described elsewhere herein, and have one or more (e.g., one, two, three , four, five, ten, fifteen, twenty, etc.) specified mutations or modification or combination of mutations or modifications.
[103] In certain embodiments of the invention, amino acid substitutions are made at one or more of the amino acid positions corresponding to th e sequence for wild type M‐MLV reverse transcriptase (SEQ ID NO:2) which are listed in Table 1 below (e.g., amino acid position 51, 67, 69, 196, 197, 200, 204, 289, 302, 306, 309, 313, 435, 454, 524, 562, 583, 594, 603, 653, and 671). In accordance with the invention , the wild type amino acids at these positions may be substituted with any other amino ac id including Ala, Arg, Asn, Arg, Asp, Cys, Gln, Glu, Gly, His, Ile, Leu, Lys, Met, Phe, Pro, Ser, Thr, Trp, Tyr, and Val. Certain illustrative amino acids at these positions are those listed in Table 1 (e.g., L/P51, S/R/N/K67, K/E69, S/P196, T/A/S/G197, N/D200, H/R204, L/M289, K/R/E/G302, T/K306, F/Y/I/N309,
F/L/C/W313, P/T330, L/V/R/G435, N/K454 D/G524, Q/E562, N/D583, N/D594, H/Q603,
H/N/D653, and L/P671. Thus, specific examples of reverse transcriptases according to the invention which exhibit increased thermostability and/o r thermoreactivity include M‐MLV reverse transcriptase in which (1) the residue at po sition 51 is proline (P) or lysine (L); (2) residue at position 67 is the serine (S), arginine (R), lysine (K) or asparagine (N); (3) the residue at position 69 is glutamic acid (E) or lysi ne (K); (4) the residue at position 196 is proline (P) or serine (S); (5) the residue at posit ion 197 is threonine (T), glycine (G), serine (S) or alanine (A); (6) the residue at position 200 is aspartic acid (D) or asparagine (N); (7) the residue at position 204 is histidine or asparagine ( R); (8) the residue at position 289 is methionine (M) or leucine (L); (9) the residue at p osition 302 is glutamic acid residue (E), lysine (K), arginine (R), or glycine (G); (10) the residue at position 306 is threonine (T) or lysine (K); (11) the residue at position 309 is phe nylalanine (F), tyrosine (Y), isoleucine (I) or asparagine (N); (12) the residue at position 313 is tryptophan (W), phenylalanine (F), leucine (L) or cysteine (C); (13) the residue at position 3 30 is tyrosine (Y) or proline (P); (14) the residue at position 435 is leucine (L), valine (V), arginine (R), or glycine (G); (15) the residue at position 454 is asparagine (N) or lysine (K); (16) the residue at position 524 is aspartic acid (D) or glycine (G); (17) the residue at position 562 is glutamic acid (E) or glutamine (Q); (18) the residue at position 583 is aspartic acid (D) or asp aragine (N); (19) the residue at position 594 is histidine (H) or glutamine (Q); (20) the residue at position 603 is leucine (L) or tryptophan (W); (21) the residue at position 653 is aspartic a cid (D), histidine (H) or asparagine (N); and (22) the residue at position 671 is leucine (L) or proline (P).
Table 1.
[104] In some embodiments, mutations or modifications in re verse transcriptases which alter thermoreactivity and/or thermostability properties may be present in conjunction with alterations which either have little or no effect on activities normally associated with reverse transcriptases (e.g., RNase H activity, reverse transc riptase or polymerase activity, terminal deoxynucleotidyl transferase (TdTase) activity, etc.) o r substantially alter one or more of these activities normally associated with reverse tran scriptases.
[105] In some embodiments, one or more mutations at a pos ition equivalent or
corresponding to positions S67, T197, and E302 of wi ld type M‐MLV (SEQ ID NO:2) reverse transcriptase can be made to produce the desired res ult (e.g., increased thermostability, increased thermoreactivity, increased efficiency (speed and processivity), increased
specificity, increased resistance to reverse transcr iptase inhibitors, and increased ability to generate cDNA from difficult RNA templates.). Thus, i n some embodiments, using amino acid positions of M‐MLV reverse transcriptase as a frame of reference, reverse transcriptases of the invention include any reverse transcriptase (e.g., M‐MLV reverse transcriptase, AMV reverse transcriptase, HIV reverse transcriptase, RSV reverse transcriptase, reverse transcriptases from viruses isolated from, for example , baboon, fowl pox, koala bear, and wild boar species) having alterations that correspond in position to one or more of the following alterations: (S67R, S67N, or S67K), (T197A, T197S, T197G), and (302K, E302R, or E302G), as well as compositions, kits, and reaction mixtures containing these mutated proteins, nucleic acid molecules which encode these p roteins, and host cells which contain these nucleic acid molecules.
[106] In other embodiments, six or more mutations at posit ions equivalent or
corresponding to positions P51, E69, P196, D200, H204 , M289, T306, F309, W313, T330, L435, N454, D524, E562, D583, H594, L603, D653, and L671 of wild type M‐MLV (SEQ ID NO:2) reverse transcriptase may be made to produce t he desired result (e.g., increased thermostability, increased thermoreactivity, increased e fficiency (speed and processivity), increased specificity, increased resistance to reverse transcriptase inhibitors, and/or increased ability to generate cDNA from difficult RNA templates.). Thus, in specific embodiments, using amino acid positions of M‐MLV re verse transcriptase as a frame of reference, reverse transcriptases of the invention inc lude any reverse transcriptase (e.g., M‐ MLV reverse transcriptase, AMV reverse transcriptase, HIV reverse transcriptase, RSV reverse transcriptase, reverse transcriptases from viruses isol ated from, for example, baboon, fowl pox, koala bear, and wild boar species) having six or more of the following alterations: P51L, E69K, P196S, D200N, H204R, M289L, T306K, (F309N, F309 Y, or F309I), (W313F, W313L, or W313C), T330P, (L435G, L435V, or L435R), N454K, D524G , E562Q, D583N, H594Q, L603W, (D653N or D653H), and L671P, as well as compositions and reaction mixtures containing these mutated proteins, nucleic acid molecules which encode these proteins, and host cells which contain these nucleic acid molecules.
[107] In other embodiments, one or more mutations at a po sition equivalent or
corresponding to positions S67, T197, and E302 and, additionally, one or more mutation at a position equivalent or corresponding to position P51, E69, P196, D200, H204, M289, T306, F309, W313, T330, L435, N454, D524, E562, D583, H594 , L603, D653, and L671 of wild type
M‐MLV (SEQ ID NO:2) reverse transcriptase may be made to produce the desired result (e.g., increased thermostability, increased thermoreactivity, i ncreased efficiency (speed and processivity), increased specificity, increased resistan ce to reverse transcriptase inhibitors, and/or increased ability to generate cDNA from diffic ult RNA templates.). Thus, in specific embodiments, using amino acid positions of M‐MLV re verse transcriptase as a frame of reference, proteins of the invention include reverse transcriptases (e.g., M‐MLV reverse transcriptase, AMV reverse transcriptase, HIV reverse transcriptase, RSV reverse
transcriptase, reverse transcriptases from viruses isol ated from, for example, baboon, fowl pox, koala bear, and wild boar species) having one or more of the following alterations: (S67R, S67N, or S67K), (T197A, T197S, T197G), and (3 02K, E302R, or E302G) and, additionally, one or more of the following alterations: P51L, E69K , P196S, D200N, H204R, M289L, T306K, (F309N, F309Y, or F309I), (W313F, W313L, or W313C), T330P, (L435G, L435V, or L435R), N454K, D524G, E562Q, D583N, H594Q, L603W, (D653N or D653H), and L671P, as well as compositions and reaction mixtures containing these mu tated proteins, nucleic acid molecules which encode these proteins, and host cells which contain these nucleic acid molecules.
[108] In other embodiments, six or more mutations at a po sition equivalent or
corresponding to positions P51, E69, P196, D200, H204 , M289, T306, F309, W313, T330, L435, N454, D524, E562, D583, H594, L603, D653, and L671 and, additionally, one or more mutation at a position equivalent or corresponding to position S67, T197, and E302 of wild type M‐MLV (SEQ ID NO:2) reverse transcriptase can be made to produce the desired result (e.g., increased thermostability, increased thermoreacti vity, increased efficiency (speed and processivity), increased specificity, increased resistan ce to reverse transcriptase inhibitors, and/or increased ability to generate cDNA from diffic ult RNA templates.). Thus, in specific embodiments, using amino acid positions of M‐MLV re verse transcriptase as a frame of reference, proteins of the invention include reverse transcriptases (e.g., M‐MLV reverse transcriptase, AMV reverse transcriptase, HIV reverse transcriptase, RSV reverse
transcriptase, reverse transcriptases from viruses isol ated from, for example, baboon, fowl pox, koala bear, and wild boar species) having six or more of the following alterations: P51L, E69K, P196S, D200N, H204R, M289L, T306K, (F309N, F309 Y, or F309I), (W313F, W313L, or W313C), T330P, (L435G, L435V, or L435R), N454K, D524G , E562Q, D583N, H594Q, L603W, (D653N or D653H), and L671P and, additionally, one o r more of the following alterations:
(S67R, S67N, or S67K), (T197A, T197S, or T197G), and (E302K, E302R, or E302G), as well as compositions and reaction mixtures containing these mu tated proteins, nucleic acid molecules which encode these proteins, and host cells which contain these nucleic acid molecules.
[109] In other embodiments, mutations at each position equi valent or corresponding to positions S67, T197, and E302 and, additionally, muta tions at each position equivalent or corresponding to position P51, E69, H204, F309, W313, T330, L435, N454, D524, D583, H594, D653, and L671 of wild type M‐MLV (SEQ ID NO:2) reverse transcriptase can be made to produce the desired result (e.g., increased thermostab ility, increased thermoreactivity, increased efficiency (speed and processivity), increase d specificity, increased resistance to reverse transcriptase inhibitors, and/or increased abil ity to generate cDNA from difficult RNA templates.). Thus, in specific embodiments, using amin o acid positions of M‐MLV reverse transcriptase as a frame of reference, proteins of t he invention include reverse transcriptases (e.g., M‐MLV reverse transcriptase, AMV reverse tran scriptase, HIV reverse transcriptase, RSV reverse transcriptase, reverse transcriptases from viruses isolated from, for example, baboon, fowl pox, koala bear, and wild boar species) having the following alterations: (S67R, S67N, or S67K), (T197A, T197S, or T197G), and (302K, E302R, or E302G) and, additionally, at P51L, E69K, H204R, (F309N, F309Y, or F309I), (W313F, W313L, or W313C), T330P, (L435G, L435V, or L435R), N454K, D524G, D583N, H594Q, (D653N or D653H), and L671P, as well as compositions and reaction mixtures containing these mu tated proteins, nucleic acid molecules which encode these proteins, and host cells which contain these nucleic acid molecules. In some embodiments, reverse transcriptase s of the invention have the following mutations: P51L, S67R, E69K, T197A, H204R, E302M, F 309N, W313F, T330P, L435G, N454K, D524G, D583N, H594QD653N, and L671P, also referred to herein as “Mut D9” (SEQ ID NO:4). [110] In some embodiments, the invention provides mutant re verse transcriptases or polypeptides having the properties described herein an d at least 70% amino acid sequence identity to SEQ ID NO:4. For example, in some emb odiments, reverse transcriptases of the invention are at least 70%, 75%, 80%, 85%, 90%, 95% , 97%, 98%, 99% or 100% identical to SEQ ID NO:4. In some embodiments, the invention pr ovides mutant reverse transcriptases or polypeptides that comprise SEQ ID NO:4. In some pref erred embodiments, the properties of the mutant reverse transcriptases or polypeptides desc ribed herein comprise one or more of the following: (a) increased thermostability; (b) in creased thermoreactivity; (c) increased
resistance to reverse transcriptase inhibitors; (d) increased speed; (e) decreased primer‐less reverse transcription; and (f) increased processivity.
[111] The corresponding positions of M‐MLV reverse transcr iptase identified above can be readily identified for other reverse transcriptases by one with skill in the art. Thus, given the defined region and the assays described in the prese nt application, one with skill in the art can make the specified modifications which would resu lt in increased thermostability, increased thermoactivity, and/or other desired features of any reverse transcriptase of interest. Identified regions of interest for other kn own reverse transcriptases and residues to be mutated in accordance with the present invention can include those listed in Figures 1A through 1D.
[112] The nucleotide sequence for wild type M‐MLV reverse transcriptase (SEQ ID NO:1) is well‐known to those skilled in the art. See, for example, Shinnick et al., 1981, Nature
293:543‐548; Georgiadis et al., 1995, Structure 3:87 9‐892), the disclosure of which is incorporated herein by reference in its entirety.
[113] In some preferred embodiments, oligonucleotide directed mutagenesis is used to create the mutant reverse transcriptases which allows for all possible classes of base pair changes at any determined site along the encoding DN A molecule. Those skilled in the art are well aware of that even when the amino acid substit uted once is replaced again with another amino acid having similar characteristics (that is, c onservative amino acid substitution), similar physiological and biochemical properties are s till observed. The effect of amino acid substitution on the various amino acid properties and protein structure and functions has been well‐studied by those in the art.
[114] In some embodiments of the present invention, the mu tant reverse transcriptases described herein demonstrate higher thermostability and /or thermoreactivity than the corresponding wild type reverse transcriptase. In some embodiments, M‐MLV mutant reverse transcriptases having the following mutations: P51L, S67R, E69K, T197A, H204R, E302K, F309N, W313F, T330P, L435G, N454K, D524G, D583 N, H594Q, D653N, and L671P, demonstrate increased thermostability at 60°C. In par ticular, in some embodiments, mutant M‐MLV reverse transcriptases as disclosed herein dem onstrate increased reverse
transcriptase activity at 60 compared to the wild type M‐MLV reverse transcrip tase as well as compared to other commercially available M‐MLV d erivative reverse transcriptases (e.g.,
Q‐SS, SSII, and SSIII) at temperatures much lowe r than 60°C (i.e., 37°C, 42°C, and 50°C, respectively). See, for example, Figure 2.
[115] In some embodiments of the present invention, the mu tant reverse transcriptases described herein demonstrate increased reverse transcri ptase activity compared to the corresponding wild type reverse transcriptase. In so me preferred embodiments, the mutant reverse transcriptases exhibit increased reverse transc riptase activity at reaction
temperatures above 37°C. For example, the mutant r everse transcriptases as described herein exhibit increased reverse transcriptase activity at reaction temperatures of 38°C, 40°C, 42°C, 45°C, 48°C, 50°C, 52°C, 55°C, 58°C, 60° C, 62°C, 65°C, 68°C, 70°C, 72°C, 75°C, 78°C, etc. See, for example, Figure 4.
[116] In some embodiments of the present invention, the mu tant reverse transcriptases described herein demonstrate increased reverse transcri ptase activity that is at least 10% more compared to the corresponding wild type reverse transcriptase. For example, the mutant reverse transcriptases as described herein exhi bit at least 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% 80%, 8 5%, 90%, 95%, 100%, etc. more reverse transcriptase activity compared to the corresp onding wild type reverse transcriptase. In some embodiments, the mutant reverse transcriptases as described herein exhibit 110%, 115%, 120%, 125%, 150%, 200%, 250%, 300%, 400%, 500% , etc. the amount of the reverse transcriptase activity exhibited by the wild type rev erse transcriptase. In some embodiments, the mutant reverse transcriptases as described herein are at least about 1.1X, 1.5X, 1.8X, 2X, 4X, 6X, 8X, 10X, 30X, 40X, 50X, etc. more thermorea ctive than the corresponding wild type reverse transcriptase. In some embodiments, the muta nt reverse transcriptases of the present invention exhibit increased activity compared to the corresponding wild type reverse transcriptase, even when the reaction or incubation t emperature of the mutant reverse transcriptase is at a higher temperature compared to the reaction or incubation temperature of the wild type polymerase.
[117] In some embodiments of the present invention, the mu tant reverse transcriptases described herein demonstrate improved or increased pro perties compared to the
corresponding wild type reverse transcriptase when bot h reverse transcriptases are at the same reaction temperature (e.g., 37°C, 40°C, 42°C, 50°C, 52°C, 55°C, 58°C, 60°C, 62°C, 65°C, 70°C, or 75°C). In some other embodiments, the m utant reverse transcriptases described herein demonstrate improved or increased properties at an elevated reaction temperature
(e.g., 52°C, 55°C, 58°C, 60°C, 62°C, 65°C, 7 0°C, 75°C) compared to the same properties demonstrated by the corresponding wild type reverse t ranscriptase at a lower temperature (e.g., 37°C, 40°C, 42°C, 50°C).
[118] In another aspect, the mutant reverse transcriptases described herein exhibit improved or increased activity (e.g., thermostability or thermoreactivity) at lower pH compared to the activity demonstrated by the correspo nding wild type reverse transcriptase under the same pH. See, for example, Figure 3.
[119] In some embodiments, the reverse transcriptases of the present invention exhibit increased activity at a wider range of pH, producing more cDNA and longer cDNA compared to a non‐mutated or conventional RTs under similar or the same conditions. For example, the mutant reverse transcriptases described herein exh ibit increased activity compared to wild type reverse transcriptase at a pH range from about from about pH 5.5 to about pH 9.0 (e.g., about pH 6.0, about pH 6.5, about pH 7.0, a bout pH 7.1, about pH 7.2, about pH 7.3, about pH 7.4, about pH 7.5, about pH 7.6, about pH 7.7, about pH 7.8, about pH 7.9, about pH 8.0, about pH 8.1, about pH 8.2, about pH 8.3, about pH 8.4, about pH 8.5, about pH 8.6, about pH 8.7, about pH 8.8, about pH 8.9, about pH 9.0, from about pH 6.0 to about pH 8.5, from about pH 6.5 to about pH 8.5, from about pH 7.0 to about pH 8.5, from about pH 7.5 to about pH 8.5, from about pH 6.0 to about pH 8.0, from about pH 6.0 to about pH 7.7, from about pH 6.0 to about pH 7.5, from about pH 6.0 t o about pH 7.0, from about pH 7.2 to about pH 7.7, from about pH 7.3 to about pH 7.7, from about pH 7.4 to about pH 7.6, from about pH 7.0 to about pH 7.4, from about pH 7.6 t o about pH 8.0, from about pH 7.6 to about pH 8.5, from about pH 7.7 to about pH 8.5, from about pH 7.9 to about pH 8.5, from about pH 8.0 to about pH 8.5, from about pH 8.2 t o about pH 8.5, from about pH 8.3 to about pH 8.5, from about pH 8.4 to about pH 8.5, from about pH 8.4 to about pH 9.0, from about pH 8.5 to about pH 9.0, etc.). In some embod iments, the mutant reverse transcriptases of the present invention exhibit at least 10% (e.g., 10%, 15%, 20%, 25%, 30%, 40%, 50%, 75%, 100%, 200%, 300%, 500%, etc.) more activity compared to the wild type RT at the same pH. In other embodiments, the mutant reverse transcriptase s of the present invention produce at least 10% (e.g., 10%, 15%, 20%, 25%, 30%, 40%, 50%, 75%, 100%, 200%, 300%, 500%, etc.) more cDNA product compared to the wild type RT at the same pH. In still other
embodiments, the mutant reverse transcriptases of the present invention produce cDNA products that are at least 10% (e.g., 10%, 15%, 20% , 25%, 30%, 40%, 50%, 75%, 100%, 200%,
300%, 500%, etc.) longer than the cDNA products p roduced by the corresponding wild type RT at the same pH. In yet other embodiments, the m utant reverse transcriptases of the present invention produce cDNA products at a rate th at is at least 10% (e.g., 10%, 15%, 20%, 25%, 30%, 40%, 50%, 75%, 100%, 200%, 300%, 500%, et c.) faster than that of the
corresponding wild type RT at the same pH. For ex ample, the mutant reverse transcriptases of the present invention produces at least 2x more (e.g., 2x, 3x, 4x, 5x, 10x, 20x, etc.) cDNA product than the corresponding wild type RT at the same pH.
[120] In some embodiments of the present invention, the mu tant reverse transcriptases described herein retain at least 20% reverse transcri ptase activity after heating to a temperature between 55°C to 75°C. For example, th e mutant reverse transcriptases retain at least 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 90%, 95%, 99% or 100% reverse transcriptase activity after heating to a temperature between 55°C to 75°C. In some embodiments, the mutant reverse transcriptases retain at least 20% reverse transcriptase activity after heating to a temperature between 55°C to 75°C for at least 5 minutes. For example, the mutant reverse transcriptase s retain at least 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 90%, 95%, 99% or 100% reverse
transcriptase activity after heating to a temperature between 55°C to 75°C for at least 5 minutes.
[121] In some embodiments of the present invention, the mu tant reverse transcriptases described herein retain at least 20% reverse transcri ptase activity after heating to a temperature between 50°C to 75°C. For example, th e mutant reverse transcriptases retain at least 20% reverse transcriptase activity after heating to a temperature of 50°C, 55°C, 58°C, 60°C, 62°C, 64°C, 68°C, 70°C, 72°C, or 75°C. In some embodiments, the mutant reverse transcriptases retain at least 20% reverse transcripta se activity after heating to a
temperature between 50°C to 75°C for at least 5 m inutes. For example, the mutant reverse transcriptases retain at least 20% reverse transcripta se activity after heating to a
temperature between a temperature of 50°C, 58°C, 60 °C, 62°C, 64°C, 68°C, 70°C, 72°C, or 75°C for at least 5 minutes.
[122] In some embodiments of the present invention, the mu tant reverse transcriptases described herein retain at least 20% reverse transcri ptase activity after heating to a temperature between 50°C to 75°C for at least 1 m inute. For example, the mutant reverse transcriptases retain at least 20% reverse transcripta se activity after heating to a
temperature between 50°C to 75°C for at least 1 minute, 2 minutes , 5 minutes, 10 minutes, 15 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, 60 minutes, etc. In some embodiments, the mutant reverse transcriptases retain at least about 20%, about 25%, about 30%, about 35%, about 40%, about 45%, about 5 0%, about 55%, about 60%, about 65%, about 70%, about 75%, about 80%, about 90%, ab out 95%, about 99% or about 100% reverse transcriptase activity after heating to a tem perature of about 50°C, about 55°C, about 58°C, about 60°C, about 62°C, about 64°C, about 68°C, about 70°C, about 72°C, or about 75°C for at least about 1 minute, about 2 m inutes, about 5 minutes, about 10 minutes, about 15 minutes, about 20 minutes, about 30 minutes , about 40 minutes, about 50 minutes, or about 60 minutes.
[123] In some embodiments of the present invention, the mu tant reverse transcriptases described herein are able to produce a cDNA that is at least 0.2 kb in length. For example, the mutant reverse transcriptases are able to produce a cDNA that is 0.2 kb, 0.5 kb, 1 kb, 1.5 kb, 2 kb, 3 kb, 4 kb, 5 kb, 6 kb, 7 kb, 7.5 kb , 8 kb, 8.5 kb, 9 kb, 9.5 kb, 10 kb, 15 kb, or 20 kb, etc. in length. In some embodiments, the mutant reve rse transcriptases described herein are able to produce a cDNA that is between about 0.2 k b to 10 kb in length. In some
embodiments, the mutant reverse transcriptases describe d herein are able to produce a cDNA that is between about 0.2 kb to 10 kb in len gth within 1 to 60 minutes at a
temperature between 25°C to 75°C. In some embodim ents, the mutant reverse
transcriptases are able to produce a cDNA that is b etween about 0.2 kb to 10 kb in length within 1 minute, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes or 60 minutes at a temperature of at least 37°C (e.g., 37°C, 40°C, 45°C, 50°C, 55°C, 60°C, 70°C or 75°C).
[124] In some preferred embodiments, the mutant or mutated reverse transcriptases of the present invention demonstrate higher thermostability th an the corresponding wild type reverse transcriptase. In particular, mutant reverse transcriptases as described herein, exhibit increased thermostability and/or increased ther moreactivity. Among some of the possible mutant reverse transcriptases provided herein, an exemplary mutant “D9” (SEQ ID NO:4) (see Figure 11) demonstrates increased thermosta bility at least 50°C. In some embodiments, at 60°C this exemplary mutant reverse t ranscriptase produces cDNA more efficiently than wild type M‐MLV reverse transcripta se at a temperature of 37°C (see, for example, Figure 2).
[125] In another aspect, the mutant reverse transcriptases as described herein are resistant to enzyme inhibitors found in biological samples, inc luding, for example, blood, sweat, tears, soil, feces, saliva, urine, and bile. Such inhibitors can include, but are not limited to, humic acid, heparin, ethanol, bile salts, fulvic acid, poly saccarides, metal ions, sodium dodecyl sulfate (SDS), EDTA, guanidinium salts, formamide, sod ium pyrophosphate, and spermidine. An inhibitor‐resistant reverse transcripatase, as use d herein, can generally refer to a reverse transcriptase that exhibits at least 10% reverse tran scriptase activity in the presence of an inhibitor(s) in the reaction mixture. For example, th e mutant reverse transcriptases described herein exhibit up to about 90% (e.g., 90%, 85%, 80% , 75%, 70%, 65%, 60%, 55%, 50%, 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10%, 5%, etc.) revers e transcriptase activity in the presence of an inhibitor compared to reactions comprising no inhibitor. The amount of inhibitor in any given reaction mixture can depend upon the type of inhibitory substance that exists within the biological sample from which the nucleic acid be ing assayed is extracted. Generally, mutant reverse transcriptases described herein (even w hen at elevated temperatures) can tolerate at least 2x (e.g., 2x, 3x, 5x, 10x, 50x, 100x) greater concentration of these inhibitory substances, as compared to the corresponding wild typ e reverse transcriptase. Assays to determine the level of inhibitory substances in a sa mple are known in the art. Inhibitor‐ resistance can be readily determined by assays descri bed herein.
Expression of Reverse Transcriptases
[126] To optimize expression of reverse transcriptases of t he present invention, inducible or constitutive promoters are well known and may be use d to express high levels of a reverse transcriptase structural gene in a recombinant host. Similarly, high copy number vectors, well known in the art, may be used to achieve high leve ls of expression. Vectors having an inducible high copy number may also be useful to en hance expression of the reverse transcriptases of the invention in a recombinant host .
[127] To express the desired structural gene in a prokaryo tic cell (such as E. coli, B. subtilis, Pseudomonas, etc.), it is preferable to operably link the desired structural gene to a functional prokaryotic promoter. However, the natural promoter of the reverse transcriptase gene may function in prokaryotic hosts allowing expre ssion of the reverse transcriptase gene. Thus, the natural promoter or other promoters may be used to express the reverse transcriptase gene. Such other promoters that may be used to enhance expression include
constitutive or regulatable (i.e., inducible or der epressible) promoters. Examples of constitutive promoters include the int promoter of ba cteriophage λ, and the bla promoter of the β‐lactamase gene of pBR322. Examples of induci ble prokaryotic promoters include the major right and left promoters of bacteriophage λ ( PR and PL), trp, recA, lacZ, lad, tet, gal, trc, ara BAD (Guzman, et al., 1995, J. Bacteriol. 1 77(14):4121‐4130) and tac promoters of E. coli. The B. subtilis promoters include α‐amylase (Ulmanen et al., J. Bacteriol 162:176‐182 (1985)) and Bacillus bacteriophage promoters (Gryczan, T., In: The Molecular Biology Of Bacilli, Academic Press, New York (1982)). Streptomyce s promoters are described by Ward et al., Mol. Gen. Genet. 203:468478 (1986)). Prokaryotic promoters are also reviewed by Glick, J. Ind. Microbiol. 1:277‐282 (1987); Cenatiempto, Y. , Biochimie 68:505‐516 (1986); and Gottesman, Ann. Rev. Genet. 18:415‐442 (1984). Expre ssion in a prokaryotic cell also requires the presence of a ribosomal binding site up stream of the gene‐encoding sequence. Such ribosomal binding sites are disclosed, for examp le, by Gold et al., Ann. Rev. Microbiol. 35:365404 (1981).
[128] To enhance the expression of reverse transcriptases o f the invention in a eukaryotic cell, well known eukaryotic promoters and hosts may be used. Enhanced expression of the reverse transcriptases may be accomplished in a proka ryotic host. One example of a prokaryotic host suitable for use with the present i nvention is Escherichia coli.
Isolation and Purification of Reverse Transcriptases
[129] The enzyme(s) of the present invention is preferably produced by growth in culture of the recombinant host containing and expressing the de sired reverse transcriptase gene. However, the reverse transcriptase of the present inv ention may be isolated from any strain, organism, or tissue which produces the reverse transc riptase of the present invention. Fragments of the reverse transcriptase are also inclu ded in the present invention. Such fragments include proteolytic fragments and fragments having reverse transcriptase activity. Such fragments may also be produced by cloning and expressing portions of the reverse transcriptase gene of interest, creating frame shift mutations and/or by adding one or more stop codons in the gene of interest for expression of a truncated protein or polypeptide. Preferably, polypeptides of the invention may be puri fied and/or isolated from a cell or organism expressing them, which may be a wild type cell or organism or a recombinant cell
or organism. In some embodiments, such polypeptides may be substantially isolated from the cell or organism in which they are expressed.
[130] Any nutrient that can be assimilated by a host cont aining the cloned reverse
transcriptase gene may be added to the culture mediu m. Optimal culture conditions should be selected case by case according to the strain us ed and the composition of the culture medium. Antibiotics may also be added to the growth media to insure maintenance of vector DNA containing the desired gene to be expressed. Med ia formulations have been described in DSM or ATCC Catalogs and Sambrook et al., In: M olecular Cloning, a Laboratory Manual (2nd ed.), Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. (1989).
[131] Recombinant host cells producing the reverse transcrip tases of this invention can be separated from liquid culture, for example, by centri fugation. In general, the collected microbial cells are dispersed in a suitable buffer, and then broken open by ultrasonic treatment or by other well‐known procedures to allo w extraction of the enzymes by the buffer solution. After removal of cell debris by ult racentrifugation or centrifugation, the reverse transcriptases can be purified by standard pr otein purification techniques such as extraction, precipitation, chromatography, affinity chro matography, electrophoresis or the like. Assays to detect the presence of the reverse transcriptase during purification are well known in the art and can be used during conventiona l biochemical purification methods to determine the presence of these enzymes.
[132] In some embodiments, reverse transcriptases of the pr esent invention may be mutated to contain an affinity tag in order to faci litate the purification of the reverse transcriptase. Suitable affinity tags are well known to those skilled in the art and include, but are not limited to, repeated sequences of amino acid s such as six histidines, epitopes such as the hemagglutinin epitope and the myc epitope, and o ther amino acid sequences that permit the simplified purification of the reverse transcripta se.
[133] The invention further provides fusion proteins compris ing (1) a protein, or fragment thereof, having one or more activity associated with a reverse transcriptase and (2) a tag (e.g., an affinity tag). In particular embodiments, t he invention includes a reverse
transcriptase (e.g., a thermostable reverse transcripta se) described herein having one or more (e.g., one, two, three, four, five, six, seven, eight, etc.) tags. These tags may be located, for example, (1) at the N‐terminus, (2) at the C terminus, or (3) at both the N‐terminus and C‐ terminus of the protein, or a fragment thereof havin g one or more activities associated with
a reverse transcriptase. A tag may also be locate d internally (e.g., between regions of amino acid sequence derived from a reverse transcriptase an d/or attached to an amino acid side chain). For example, Ferguson et al., Protein Sci. 7 :1636‐1638 (1998), describe a siderophore receptor, FhuA, from Escherichia coli into which an affinity tag (i.e., a hexahistidine sequence) was inserted. This tag was shown to functi on in purification protocols employing metal chelate affinity chromatography. Additional fusio n proteins with internal tags are described in U.S. Pat. No. 6,143,524, the entire dis closure of which is incorporated herein by reference.
[134] Tags used to prepare compositions of the invention m ay vary in length but will typically be from about 5 to about 500, from about 5 to about 100, from about 10 to about 100, from about 15 to about 100, from about 20 to about 100, from about 25 to about 100, from about 30 to about 100 from about 35 to about 100, from about 40 to about 100, from about 45 to about 100, from about 50 to about 100, from about 55 to about 100, from about 60 to about 100, from about 65 to about 100, from about 70 to about 100, from about 75 to about 100, from about 80 to about 100, from about 85 to about 100, from about 90 to about 100, from about 95 to about 100, from about 5 to about 80, from about 10 to about 80, from about 20 to about 80, from about 30 to about 80, from about 40 to about 80, from about 50 to about 80, from about 60 to about 80, from about 70 to about 80, from about 5 to about 60, from about 10 to about 60, from about 20 to a bout 60, from about 30 to about 60, from about 40 to about 60, from about 50 to about 60, from about 5 to about 40, from about 10 to about 40, from about 20 to about 40, from about 30 to about 40, from about 5 to about 30, from about 10 to about 30, from about 20 to a bout 30, from about 5 to about 25, from about 10 to about 25, or from about 15 to about 2 5 amino acid residues in length.
[135] Tags used to prepare compositions of the invention i nclude those which contribute to the thermostability of the fusion protein. Thus, thes e tags may be at least partly responsible, for example, for a particular protein (e.g., a prote in having one or more activities of a reverse transcriptase activity) having increased thermostability . Examples of tags that enhance the thermostability of a reverse transcriptase (i.e., M‐ MLV reverse transcriptase) include, but are not limited to, tags having the following amino acid sequences:
MGGSHHHHHHGMASMTGGQQMGRDLYDDDDKH and MASGTGGQQMGRDLYDDDDKH . Fragments of these tags may also be used in accorda nce with the invention (preferably those having 3 or more, 5 or more, 10 or more, or 15 o r more amino acids) Thus, the invention
includes, in part, reverse transcriptases, or fragm ents thereof that comprise tags and demonstrate enhanced thermostability. Using well known methods, one of skill in the art can attach one or more of above‐mentioned tags to one or more RT enzymes, or fragments thereof having reverse transcriptase activity, to prod uce a thermostable reverse
transcriptase enzyme or fragment thereof.
[136] Tags used in the practice of the invention may serv e any number of purposes and a number of tags may be added to impart one or more different functions to the reverse transcriptase of the invention. For example, tags may (1) contribute to protein‐protein interactions both internally within a protein and wit h other protein molecules, (2) make the protein amenable to particular purification methods, ( 3) enable one to identify whether the protein is present in a composition; or (4) give th e protein other functional characteristics. [137] Examples of tags which may be used in the practice of the invention include metal binding domains (e.g., a poly‐histidine segments suc h as a three, four, five, six, or seven histidine region), immunoglobulin binding domains (e.g. , (1) Protein A; (2) Protein G; (3) T cell, B cell, and/or Fc receptors; and/or (4) comple ment protein antibody‐binding domain); sugar binding domains (e.g., a maltose binding domain , chitin‐binding domain); and detectable domains (e.g., at least a portion of beta ‐galactosidase). Fusion proteins may contain one or more tags such as those described ab ove. Typically, fusion proteins that contain more than one tag will contain these tags a t one terminus or both termini (i.e., the N‐terminus and the C‐terminus) of the reverse tra nscriptase, although one or more tags may be located internally instead of or in addition to those present at termini. Further, more than one tag may be present at one terminus, internally and/or at both termini of the reverse transcriptase. For example, three consecutive tags cou ld be linked end‐to‐end at the N‐ terminus of the reverse transcriptase. The invention further include compositions and reaction mixture which contain the above fusion prote ins, as well as methods for preparing these fusion proteins, nucleic acid molecules (e.g., vectors) which encode these fusion proteins and recombinant host cells which contain the se nucleic acid molecules. The invention also includes methods for using these fusio n proteins as described elsewhere herein (e.g., methods for reverse transcribing nucleic acid molecules).
[138] Tags which enable one to identify whether the fusion protein is present in a
composition include, for example, tags which can be used to identify the protein in an
electrophoretic gel. A number of such tags are kn own in the art and include epitopes and antibody binding domains which can be used for Weste rn blots.
[139] The amino acid composition of the tags for use in the present invention may vary. In some embodiments, a tag may contain from about 1% t o about 5% amino acids that have a positive charge at physiological pH, e.g., lysine, ar ginine, and histidine, or from about 5% to about 10% amino acids that have a positive charge a t physiological pH, or from about 10% to about 20% amino acids that have a positive charge a t physiological pH, or from about 10% to about 30% amino acids that have a positive charge a t physiological pH, or from about 10% to about 50% amino acids that have a positive charge a t physiological pH, or from about 10% to about 75% amino acids that have a positive charge a t physiological pH. In some
embodiments, a tag may contain from about 1% to abo ut 5% amino acids that have a negative charge at physiological pH, e.g., aspartic a cid and glutamic acid, or from about 5% to about 10% amino acids that have a negative charge a t physiological pH, or from about 10% to about 20% amino acids that have a negative charg e at physiological pH, or from about 10% to about 30% amino acids that have a negative charge at physiological pH, or from about 10% to about 50% amino acids that have a neg ative charge at physiological pH, or from about 10% to about 75% amino acids that have a negative charge at physiological pH. In some embodiments, a tag may comprise a sequence of amino acids that contains two or more contiguous charged amino acids that may be the same or different and may be of the same or different charge. For example, a tag may co ntain a series (e.g., two, three, four, five, six, ten etc.) of positively charged amino acids tha t may be the same or different. A tag may contain a series (e.g., two, three, four, five, six, ten etc.) of negatively charged amino acids that may be the same or different. In some embodime nts, a tag may contain a series (e.g., two, three, four, five, six, ten etc.) of alternatin g positively charged and negatively charged amino acids that may be the same or different (e.g. , positive, negative, positive, negative, etc.). Any of the above‐described series of amino acids (e.g., positively charged, negatively charged or alternating charge) may comprise one or m ore neutral polar or non‐polar amino acids (e.g., two, three, four, five, six, ten etc.) spaced between the charged amino acids. Such neutral amino acids may be evenly distributed through out the series of charged amino acids (e.g., charged, neutral, charged, neutral) or may be unevenly distributed throughout the series (e.g., charged, a plurality of neutral, charge d, neutral, a plurality of charged, etc.). In some embodiments, tags to be attached to the polypep tides of the invention may have an
overall charge at physiological pH (e.g., positive charge or negative charge). The size of the overall charge may vary, for example, the tag may c ontain a net plus one, two, three, four, five, etc. or may possess a net negative one, two, three, four, five, etc. The present invention also provides reverse transcriptases (e.g., thermostabl e reverse transcriptases) comprising one or more of the above‐described tag sequences, vectors encoding such reverse transcriptases, host cells reaction mixture, compositio ns and reaction mixtures comprising such reverse transcriptases, as well as kits comprisi ng containers containing such reverse transcriptases.
[140] In some embodiments, it may be desirable to remove all or a portion of a tag
sequence from a fusion protein comprising a tag sequ ence and a sequence having reverse transcriptase (RT) activity. In embodiments of this t ype, one or more amino acids forming a cleavage site, e.g., for a protease enzyme, may be incorporated into the primary sequence of the fusion protein. The cleavage site may be located such that cleavage at the site may remove all or a portion of the tag sequence from t he fusion protein. In some embodiments, the cleavage site may be located between the tag se quence and the sequence having RT activity such that all of the tag sequence is remov ed by cleavage with a protease enzyme that recognizes the cleavage site. Examples of suitable cl eavage sites include, but are not limited to, the Factor Xa cleavage site having the sequence Ile‐Glu‐Gly‐Arg, which is recognized and cleaved by blood coagulation factor Xa, and the thro mbin cleavage site having the sequence Leu‐Val‐Pro‐Arg, which is recognized and cleaved by thrombin. Other suitable cleavage sites are known to those skilled in the art and may be used in conjunction with the present invention.
[141] In some embodiments, the reverse transcriptases of th e invention have specific activities (e.g., RNA‐directed DNA polymerase activit y and/or RNase H activity) greater than about 5 units/mg, preferably greater than about 50 u nits/mg, more preferably greater than about 100 units/mg, 250 units/mg, 500 units/mg, 1000 units/mg, 5000 units/mg or 10,000 units/mg, and most preferably greater than about 15,0 00 units/mg, greater than about 16,000 units/mg, greater than about 17,000 units/mg, greater than about 18,000 units/mg, greater than about 19,000 units/mg and greater than about 20,000 units/mg. In some embodiments, the reverse transcriptases of the present invention may have specific activities greater than about 50,000 units/mg, greater than abou t 100,000 units/mg, greater than about 150,000 units/mg, greater than about 200,000 un its/mg, greater than about 250,000
units/mg and greater than about 300,000 units/mg. Preferred ranges of specific activities for the reverse transcriptases of the invention include a specific activity from about 5 units/mg to about 750,000 units/mg, a specific activity from about 5 units/mg to about 500,000 units/mg, from about 5 units/mg to about 300,000 uni ts/mg, a specific activity of from about 50 units/mg to about 750,000 units/mg, a specific ac tivity from about 100 units/mg to about 750,000 units/mg, a specific activity from about 250 units/mg to about 750,000 units/mg, a specific activity from about 500 units/mg to about 7 50,000 units/mg, a specific activity from about 1000 units/mg to about 750,000 units/mg, a spe cific activity from about 5000 units/mg to about 750,000 units/mg, a specific activi ty from about 10,000 units/mg to about 750,000 units/mg, a specific activity from about 25,0 00 units/mg to about 750,000 units/mg, a specific activity from about 100 units/mg to about 500 units/mg, a specific activity from about 100 units/mg to about 400 units/mg, and a spe cific activity from about 200 units/mg to about 500 units/mg. Other preferred ranges of spe cific activities include a specific activity of from about 200,000 units/mg to about 350,000 unit s/mg, a specific activity from about 225,000 units/mg to about 300,000 units/mg, a specifi c activity from about 250,000 units/mg to about 300,000 units/mg, a specific activity of fr om about 200,000 units/mg to about 750,000 units/mg, a specific activity of from about 200,000 units/mg to about 500,000 units/mg, a specific activity of from about 200,000 units/mg to about 400,000 units/mg, a specific activity of from about 250,000 units/mg to about 750,000 units/mg, a specific activity of from about 250,000 units/mg to about 500,000 unit s/mg, and a specific activity of from about 250,000 units/mg to about 400,000 units/mg. Pre ferably, the lower end of the specific activity range may vary from 50, 100, 200, 300, 400 , 500, 700, 900, 1,000, 5,000, 10,000, 20,000, 30,000, 35,000, 40,000, 45,000, 50,000, 55,000 , 60,000, 65,000, 70,000, 75,000, and 80,000 units/mg, while the upper end of the range m ay vary from 750,000, 650,000, 600,000, 550,000, 500,000, 450,000, 400,000, 350,000, 300,000, 250,000, 200,000, 150,000, 140,000, 130,000, 120,000, 110,000, 100,000, and 90,000 units/m g. Specific activity may be determined using enzyme assays and protein assays wel l known in the art. DNA polymerase assays and RNase H assays are described, for example , in U.S. Pat. No. 5,244,797 and WO 98/47912, the disclosures of which are fully incorpor ated herein by reference. In some embodiments of the present invention, the specific ac tivity of the thermostable reverse transcriptase prepared in accordance with the present invention may be higher than the specific activity of a non‐thermostable (e.g., wild type) reverse transcriptase. In some
embodiments, the specific activity of the thermosta ble reverse transcriptase may be 5%, 10,%, 15%, 20%, 25%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% or more higher than the specific activity of a corresponding non‐thermostable reverse transcriptase. In some preferred embodiments, the specific activity of the t hermostable reverse transcriptase according to the present invention may be 30% or mo re than the specific activity of a corresponding non‐thermostable reverse transcriptase. In accordance with the invention, specific activity is a measurement of the enzymatic activity (in units) of the protein or enzyme relative to the total amount of protein or e nzyme used in a reaction. The
measurement of a specific activity may be determined by standard techniques well‐known to one of ordinary skill in the art.
Compositions and Reaction Mixtures Comprising Revers e Transcriptases
[142] The present teachings provide compositions comprising a variety of components in various combinations. In some embodiments of the pr esent invention, the compositions are formulated by admixing one or more reverse transcript ases a in a buffered salt solution. One or more DNA polymerases and/or one or more nucleotid es, and/or one or more primers may optionally be added to make the compositions of the invention. These compositions can be used in the present methods to produce, analyze, qua ntitate and otherwise manipulate nucleic acid molecules (e.g., using reverse transcript ion or one‐step (coupled) RT‐PCR procedures).
[143] In some embodiments, the enzymes are provided at wor king concentrations (e.g., 1x) in stable buffered salt solutions. The terms “stabl e” and “stability” as used herein generally mean the retention by a composition, such as an enz yme composition, of at least 70%, preferably at least 80%, and most preferably at leas t 90%, of the original enzymatic activity (in units) after the enzyme or composition containing the enzyme has been stored for about one week at a temperature of about 4°C, about two to six months at a temperature of about −20° C., and about six months or longer at a te mperature of about −80°C. As used herein, the term “working concentration” means the concentratio n of an enzyme that is at or near the optimal concentration used in a solution to perform a particular function (such as reverse transcription of nucleic acids).
[144] Such compositions can also be formulated as concentra ted stock solutions (e.g., 2x, 3x, 4x, 5x, 6x, 10x, etc.). In some embodiments, ha ving the composition as a concentrated (e.g., 5x) stock solution allows a greater amount of nucleic acid sample to be added (such as, for example, when the compositions are used for nucl eic acid synthesis).
[145] The water used in forming the compositions of the p resent invention is preferably distilled, deionized and sterile filtered (through a 0.1‐0.2 micrometer filter), and is free of contamination by DNase and RNase enzymes. Such water is available commercially, for example from Life Technologies (Carlsbad, CA), or may be made as needed according to methods well known to those skilled in the art.
[146] In addition to the enzyme components, the present co mpositions can comprise one or more buffers and cofactors necessary for synthesis of a nucleic acid molecule such as a cDNA molecule. In some embodiments, buffers for use in forming the present compositions are the acetate, sulfate, hydrochloride, phosphate or free acid forms of Tris‐
(hydroxymethyl)aminomethane (TRIS®) or 4‐(2‐hydroxye thyl)‐1‐piperazineethanesulfonic acid (HEPES), although alternative buffers of the sam e approximate ionic strength and pKa as TRIS® or HEPES may be used with equivalent results. For example, possible buffers for use with the described enzymes can include, but are not limited to 3‐
{[tris(hydroxymethyl)methyl]amino} propanesulfonic acid ( TAPS), N,N‐bis(2‐
hydroxyethyl)glycine (Bicine), (hydroxymethyl)methylamine (Tris), N‐
tris(hydroxymethyl)methylglycine (Tricine), 3‐[N‐Tris( hydroxymethyl)methylamino]‐2‐ hydroxypropanesulfonic Acid (TAPSO), 4‐2‐hydroxyethyl ‐1‐piperazineethanesulfonic acid (HEPES), 2‐ {[tris(hydroxymethyl)methyl]amino} ethanesu lfonic acid (TES), 3‐(N‐
morpholino)propanesulfonic acid (MOPS), piperazine‐N,N bis(2‐ethanesulfonic acid) (PIPES), and dimethylarsinic acid (cacodylate).
[147] In addition to buffer salts, cofactor salts such as those of potassium (preferably potassium chloride or potassium acetate) and magnesium (preferably magnesium chloride or magnesium acetate) are contemplated for use in the c ompositions of the invention.
[148] Addition of one or more carbohydrates and/or sugars to the compositions and/or synthesis reaction mixtures may also be advantageous, to support enhanced stability of the compositions upon storage and/or reaction mixtures dur ing synthesis. In some
embodiments, carbohydrates or sugars for inclusion in the compositions and/or synthesis reaction mixtures of the invention include, but are not limited to, sucrose, trehalose,
glycerol, and the like. In some embodiments, treha lose is provided at concentrations ranging from 0.01M to 5M (e.g., 0.01 M, 0.05 M, 0.1 M, 0. 5 M, 0.75 M, 1.0 M, 2.0 M, 3.0 M, 4.0 M or 5.0 M). In some embodiments, glycerol is provided at concentrations ranging from 5% to 60%. (e.g., 5%, 10%, 15%, 25%, 30%, 40%, 50%, 60%). Furthermore, such carbohydrates and/or sugars may be added to the storage buffers f or the enzymes used in the production of the enzyme compositions and kits of the invention an d may be provided in compositions that are either in liquid or dry form (e.g., lyophilized) . Such carbohydrates and/or sugars are commercially available from a number of sources, incl uding Sigma (St. Louis, Mo.).
[149] Likewise, addition of one or more surfactants and/or detergents to the compositions and/or synthesis reaction mixtures may also be advant ageous, to support enhanced stability of the compositions and/or reaction mixtures upon sto rage. Preferred such detergents for inclusion in the compositions and/or synthesis reactio n mixtures of the invention include, but are not limited to Tween 20, Nonidet P 40 (NP‐40) , Brij58, CHAPS, Big CHAPS, CHAPS, and the like. Other surfactants or detergents, such as thos e described in pending U.S. Application Nos. 13/492,576 and 61/895,876 (the disclosures of wh ich are incorporated herein by reference in their entirety) may also be included in the compositions and/or synthesis reaction mixtures of the invention. Furthermore, such detergents may be added to the storage buffers for the enzymes used in the producti on of the enzyme compositions and kits of the invention. Examples of such detergents are co mmercially available from a number of sources, including Sigma (St. Louis, Mo.).
[150] It is often preferable to first dissolve the buffer salts, cofactor salts, carbohydrates or sugars, or detergents at working concentrations in wa ter and to adjust the pH of the solution prior to addition of the enzymes. In this way, the pH‐sensitive enzymes will be less subject to acid‐ or alkaline‐mediated inactivation during form ulation of the present compositions. Thus, in some embodiments, buffered salt solutions are form ulated by combining a buffer salt such as a salt of Tris(hydroxymethyl)aminomethane (TRIS®) or the hydrochloride salt thereof, with a sufficient quantity of water. In some embodiments , this combination yields a solution having a TRIS® concentration of 5‐150 millimolar, preferably 10‐60 millimolar, and most preferably about 20‐60 millimolar. To this solution, a salt of magnesium (preferably either the chloride or acetate salt thereof) or other dival ent cation, may be added to provide a working concentration thereof of 1‐10 millimolar, pr eferably 1.5‐8.0 millimolar, and most preferably about 3‐7.5 millimolar. A salt of potass ium (preferably a chloride or acetate salt of
potassium), or other monovalent cation (e.g., Na), may also be added to the solution, at a working concentration of 10‐100 millimolar and most preferably about 75 millimolar. A reducing agent, such as dithiothreitol, may be added to the solution, preferably at a final concentration of about 1‐100 mM, more preferably a concentration of about 5‐50 mM or about 7.5‐20 mM, and most preferably at a concentr ation of about 10 mM. Preferred concentrations of carbohydrates and/or sugars for incl usion in the compositions of the invention range from about 5% (w/v) to about 30% (w /v), from about 7.5% (w/v) to about 25% (w/v), from about 10% (w/v) to about 25% (w/v), from about 10% (w/v) to about 20% (w/v), and preferably from about 10% (w/v) to about 15% (w/v). Preferred concentrations of surfactants and/or detergents for inclusion in the co mpositions of the invention range from about 0.001% (w/v) to about 5% (w/v), from about 0. 002% (w/v) to about 2% (w/v), from about 0.004% (w/v) to about 1% (w/v), from about 0. 01% (w/v) to about 0.5% (w/v), and preferably from about 0.05% (w/v) to about 0.1% (w/v ). A small amount of a salt of ethylenediaminetetraacetate (EDTA), such as disodium ED TA, may also be added (preferably about 0.1 millimolar). In some embodiments, after add ition of all buffers and salts, this buffered salt solution is mixed well until all salts are dissolved, and the pH is adjusted using methods known in the art. In some embodiments, the final buffer pH ranges from about 6.0 to about 9.5, from about 6.9 to about 8.7, or from about 7.3 to about 8.3.
[151] To these buffered salt solutions, the enzymes (revers e transcriptases) are added to produce the compositions of the present invention. In some embodiments, reverse transcriptases are added at a working concentration i n the solution of from about 1,000 to about 50,000 units per milliliter, from about 2,000 to about 30,000 units per milliliter, from about 2,500 to about 25,000 units per milliliter, fr om about 3,000 to about 22,500 units per milliliter, from about 4,000 to about 20,000 units p er milliliter, or from about 5,000 to about 20,000 units per milliliter. In some embodiments, a reverse transcriptases of the invention (e.g., an M‐MLV reverse transcriptase) may be added at a working concentration described above in a first strand reaction mixture (e.g., a r eaction to reverse transcribe an mRNA molecule) and/or in a reverse transcription coupled w ith a polymerase chain reaction. A suitable concentration of a reverse transcriptase of the invention for these reactions may be from about 5,000 units/ml to about 50,000 units/ml, from about 5,000 units/ml to about 40,000 units/ml, from about 5,000 units/ml to about 30,000 units/ml, or from about 5,000 units/ml to about 20,000 units/ml of reverse transcri ptase. A reaction may be conducted in a
volume of 20 μl to 50 μl and such a reaction may contain 50 units, 100, units, 200 units, 300 units, 400 units or more of a reverse transcriptase of the invention. Those skilled in the art will appreciate that adding additional reverse transcr iptase may allow increased synthesis of the first strand (e.g., the DNA strand complementary to the mRNA strand) at the expense of increased enzyme usage. The skilled artisan can deter mine without undue experimentation the amount of a reverse transcriptase of the inventi on to add to a reaction in order to produce a desired amount of product at an acceptable expense.
[152] In some embodiments, mutant reverse transcriptases des cribed herein are provided at a working concentration in solution from about 10 0 to about 5000 units per milliliter, from about 125 to about 4000 units per milliliter, from about 150 to about 3000 units per milliliter, from about 200 to about 2500 units per milliliter, from about 225 to about 2000 units per milliliter, and most preferably at a working concentr ation of from about 250 to about 1000 units per milliliter. The enzymes may be added to t he solution in any order, or may be added simultaneously.
[153] The compositions of the invention may further compris e one or more nucleotides, which are preferably deoxynucleoside triphosphates (dNT Ps) or dideoxynucleoside triphosphates (ddNTPs). The dNTP components of the pr esent compositions serve as the “building blocks” for newly synthesized nucleic ac ids, being incorporated therein by the action of the polymerases, and the ddNTPs may be us ed in sequencing methods according to the invention. Examples of nucleotides suitable for u se in the present compositions include, but are not limited to, dUTP, dATP, dTTP, dCTP, dGT P, dITP, 7‐deaza‐dGTP, α‐thio‐dATP, α‐ thio‐dTTP, α‐thio‐dGTP, α‐thio‐dCTP, ddUTP, ddATP, ddTTP, ddCTP, ddGTP, ddITP, 7‐deaza‐ ddGTP, α‐thio‐ddATP, α‐thio‐ddTTP, α‐thio‐ ddGTP, α‐thio‐ddCTP or derivatives thereof, all o f which are available commercially from sources includin g Invitrogen Corporation (Carlsbad, Calif.), New England BioLabs (Beverly, Mass.) and Sig ma Chemical Company (Saint Louis, Mo.). The nucleotides may be unlabeled, or they may be detectably labeled by coupling them by methods known in the art with radioisotopes (e.g. , 3 H, 14 C, 32 P or 35 S), vitamins (e.g., biotin), fluorescent moieties (e.g., fluorescein, rhoda mine, Texas Red, or phycoerythrin), chemiluminescent labels (e.g., using the PHOTO‐GENE or ACES™ chemiluminescence systems, available commercially from Life Technologies (Carlsbad, Calif.)), dioxigenin and the like. Labeled nucleotides may also be obtained commer cially, for example from Life
Technologies (Carlsbad, Calif.) or Sigma Chemical Comp any (Saint Louis, Mo.). In some
embodiments of the present compositions, the nucleo tides are added to give a working concentration of each nucleotide of about 10‐4000 m icromolar, about 50‐2000 micromolar, about 100‐1500 micromolar, or about 200‐1200 micro molar, or about 1000 micromolar. [154] In accordance with the present teachings, one or mor e agents can also be added to the present compositions to assist in overcoming the inhibition of RT reactions by a variety of compounds often found in samples used for nucleic ac id preparation, isolation or
purification. Such inhibitors can include, for example , heparin (blood); hematin (blood); EDTA (blood); citrate (blood); immunoglobin G (blood, serum ); humic acid (soil, feces); lactoferrin (milk, saliva, other secretory fluids); urea (urine); plant polysaccharides (plants); melanin (skin, hair); myoglobin (tissue); and indigo dye (tex tiles). Such agents for use in overcoming RT inhibition can include proteins such as, but not limited to, albumin (e.g. bovine serum albumin (BSA), recombinant BSA and albumins derived f rom other species), α‐lacalbumin, β‐ lactoblogulin, casein, apotransferrin, spermine, gelatin (e.g., human recombinant gelatin, fish gelatin and gelatins derived from other species), and DNA‐binding proteins (e.g., phage T4 gene 32 (T4gP32)), or peptide or polypeptide variants , fragments or derivatives thereof. Other non‐protein based PCR inhibitor blocking agent s for use in the present teachings can include, for example, deferoxamine mesylate. Some pref erred proteins for use as PCR inhibitor blocking agents include bovine serum albumin (BSA), fish gelatin, and T4gP32 proteins. In some embodiments, anti‐RT inhibitor age nts are added to the present compositions to give a final concentration in a work ing solution of about 1 ng/μL to about 10,000 ng/μL, about 50 ng/μL to about 8000 ng/μL, about 100 ng/μL to about 6000 ng/μL, about 200 ng/μL to about 5000 ng/μL or preferably about 500 ng/μL to about 3000 ng/μL. Anti‐RT inhibitor agents can also be added as a p ercentage of the final concentration in a working solution, for example, from about 0.001% to about 15%, about 0.05% to about 10%, about 0.01% to about 5%, or preferably about 0.1% t o about 1%. The addition of these anti‐ RT inhibitor agents, both individually or in combinat ion, can increase tolerance to such RT inhibitor contaminants. Thus, the present compositions can further comprise agents that work alone or in combination to increase tolerance t o various inhibitors including, for example, ethanol, bile salts, humic acid, hematin, an d heparin.
[155] In some embodiments, component deterioration can be r educed by storage of the reagent compositions at a temperature of about ‐80 C (for up to two years) or at a temperature of about −20° C (for up to one year) .
[156] In some embodiments, the present compositions can be packaged in a suitable container or vessel capable of holding the compositio n and which will not significantly interact with components of the composition. The cont ainer or vessel can be designed to permit easy dispensing of the dosage form by individ uals or by a liquid handling instrument. The containers or vessels of such composition can be further packaged into multi‐pack units. [157] In another aspect, the compositions and reverse trans criptases of the invention may be prepared and stored in dry form (e.g., lyophilize d) in the presence of one or more carbohydrates, sugars, or synthetic polymers. Preferred carbohydrates, sugars or polymers for the preparation of dried compositions or reverse transcriptases include, but are not limited to, sucrose, trehalose, and polyvinylpyrrolidon e (PVP) or combinations thereof. See, e.g., U.S. Pat. Nos. 5,098,893, 4,891,319, and 5,556, 771, the disclosures of which are entirely incorporated herein by reference. Such dried compositi ons and enzymes may be stored at various temperatures for extended times without signif icant deterioration of enzymes or components of the compositions of the invention. In some preferred embodiments, the dried reverse transcriptases or compositions are store d at about −20°C to about 25°C.
[158] The invention further includes compositions for revers e transcribing nucleic acid molecules, as well as reverse transcription methods e mploying such compositions and product nucleic acid molecules produced using such me thods. In many instances,
compositions of the invention may contain one or mor e of the following components: (1) one or more buffering agent (e.g., sodium phosphate, sodi um acetate, 2‐(N‐morpholino)‐ ethanesulfonic acid (MES), tris‐(hydroxymethyl)aminomet hane (Tris), 3‐(cyclohexylamino)‐2‐ hydroxy‐1‐propanesulfonic acid (CAPS), citrate, N‐ 2‐hydroxyethylpiperazine‐N‐2‐
ethanesulfonic acid (HEPES), acetate, 3‐(N‐morpholin o)propanesulfonic acid (MOPS), N‐ tris(hydroxymethyl)methyl‐3‐aminopropanesulfonio acid (TAPS), etc.), (2) one or more monovalent cationic salt (e.g., NaCl, KCl, etc.), (3) one or more divalent cationic salt (e.g., MnCl2, MgCl2, MgSO4, CaCl2, etc.), (4) one or more reducing agent (e.g., dithiothreitol, β‐ mercaptoethanol, etc.), (5) one or more ionic or non ‐ionic detergent (e.g., TRITON X‐100™, NONIDET P40™, sodium dodecyl sulphate, etc.), (6) o ne or more DNA polymerase inhibitor (e.g., Actinomycin D, etc.), (7) nucleotides (e.g., d NTPs, such as dGTP, dATP, dCTP, dTTP, etc.), (8) RNA to be reverse transcribed and/or amplified, (9) one or more RNase inhibitor (e.g., RNASEOUT™, Invitrogen Corporation, Carlsbad, Calif., catalog number 10777‐019 etc.), (10) a reverse transcriptase (e.g., a reverse transcriptase o f the invention, and/or (11) one or more
diluent (e.g., water). Other components and/or cons tituents (e.g., primers, DNA polymerases, etc.) may also be present in composition s. In certain embodiments, compositions used for sequencing may contain one or more of the following components: (1) a single‐ stranded RNA template, (2) a primer, (3) nucleotides, (4) a label such as a radioactive label conjugated with the nucleotide base or a fluorescent label conjugated to the primer, and/or (5) a terminating agent, such as a chain terminator base comprising a dideoxynucleotide (ddATP, ddGTP, ddCTP, or ddTTP.
[159] The concentration of the buffering agent in the comp ositions of the invention will vary with the particular buffering agent used. Typica lly, the working concentration (i.e., the concentration in the reaction mixture) of the bufferi ng agent will be from about 5 mM to about 500 mM (e.g., about 10 mM, about 15 mM, abou t 20 mM, about 25 mM, about 30 mM, about 35 mM, about 40 mM, about 45 mM, about 50 mM, about 55 mM, about 60 mM, about 65 mM, about 70 mM, about 75 mM, about 80 m M, about 85 mM, about 90 mM, about 95 mM, about 100 mM, from about 5 mM to abo ut 500 mM, from about 10 mM to about 500 mM, from about 20 mM to about 500 mM, f rom about 25 mM to about 500 mM, from about 30 mM to about 500 mM, from about 40 m M to about 500 mM, from about 50 mM to about 500 mM, from about 75 mM to about 500 mM, from about 100 mM to about 500 mM, from about 25 mM to about 50 mM, from abo ut 25 mM to about 75 mM, from about 25 mM to about 100 mM, from about 25 mM to about 200 mM, from about 25 mM to about 300 mM, etc.). When Tris (e.g., Tris‐HCl) is used, the Tris working concentration will typically be from about 5 mM to about 100 mM, from about 5 mM to about 75 mM, from about 10 mM to about 75 mM, from about 10 mM to about 60 mM, from about 10 mM to about 50 mM, from about 25 mM to about 50 mM, etc .
[160] The final pH of solutions of the invention will gen erally be set and maintained by buffering agents present in compositions of the inven tion. The pH of compositions of the invention, and hence reaction mixtures of the inventi on, will vary with the particular use and the buffering agent present but will often be from about pH 5.5 to about pH 9.0 (e.g., about pH 6.0, about pH 6.5, about pH 7.0, about pH 7.1, about pH 7.2, about pH 7.3, about pH 7.4, about pH 7.5, about pH 7.6, about pH 7.7, about pH 7.8, about pH 7.9, about pH 8.0, about pH 8.1, about pH 8.2, about pH 8.3, about pH 8.4, about pH 8.5, about pH 8.6, about pH 8.7, about pH 8.8, about pH 8.9, about pH 9.0, from abo ut pH 6.0 to about pH 8.5, from about pH 6.5 to about pH 8.5, from about pH 7.0 to about p H 8.5, from about pH 7.5 to about pH 8.5,
from about pH 6.0 to about pH 8.0, from about p H 6.0 to about pH 7.7, from about pH 6.0 to about pH 7.5, from about pH 6.0 to about pH 7.0, from about pH 7.2 to about pH 7.7, from about pH 7.3 to about pH 7.7, from about pH 7.4 t o about pH 7.6, from about pH 7.0 to about pH 7.4, from about pH 7.6 to about pH 8.0, from about pH 7.6 to about pH 8.5, from about pH 7.7 to about pH 8.5, from about pH 7.9 t o about pH 8.5, from about pH 8.0 to about pH 8.5, from about pH 8.2 to about pH 8.5, from about pH 8.3 to about pH 8.5, from about pH 8.4 to about pH 8.5, from about pH 8.4 t o about pH 9.0, from about pH 8.5 to about pH 9.0, etc.)
[161] As indicated, one or more monovalent cationic salts (e.g., NaCl, KCl, etc.) may be included in compositions of the invention. In many i nstances, salts used in compositions of the invention will dissociate in solution to generate at least one species which is monovalent (e.g., Na+, K+, etc.) When included in compositions of the invention, salts will often be present either individually or in a combined concentr ation of from about 0.5 mM to about 500 mM (e.g., about 1 mM, about 2 mM, about 3 mM, about 5 mM, about 10 mM, about 12 mM, about 15 mM, about 17 mM, about 20 mM, about 22 mM, about 23 mM, about 24 mM, about 25 mM, about 27 mM, about 30 mM, about 35 m M, about 40 mM, about 45 mM, about 50 mM, about 55 mM, about 60 mM, about 64 m M, about 65 mM, about 70 mM, about 75 mM, about 80 mM, about 85 mM, about 90 m M, about 95 mM, about 100 mM, about 120 mM, about 140 mM, about 150 mM, about 17 5 mM, about 200 mM, about 225 mM, about 250 mM, about 275 mM, about 300 mM, abou t 325 mM, about 350 mM, about 375 mM, about 400 mM, from about 1 mM to about 50 0 mM, from about 5 mM to about 500 mM, from about 10 mM to about 500 mM, from ab out 20 mM to about 500 mM, from about 30 mM to about 500 mM, from about 40 mM to about 500 mM, from about 50 mM to about 500 mM, from about 60 mM to about 500 mM, f rom about 65 mM to about 500 mM, from about 75 mM to about 500 mM, from about 85 m M to about 500 mM, from about 90 mM to about 500 mM, from about 100 mM to about 50 0 mM, from about 125 mM to about 500 mM, from about 150 mM to about 500 mM, from a bout 200 mM to about 500 mM, from about 10 mM to about 100 mM, from about 10 mM to about 75 mM, from about 10 mM to about 50 mM, from about 20 mM to about 200 mM, fr om about 20 mM to about 150 mM, from about 20 mM to about 125 mM, from about 20 m M to about 100 mM, from about 20 mM to about 80 mM, from about 20 mM to about 75 mM, from about 20 mM to about 60 mM, from about 20 mM to about 50 mM, from about 3 0 mM to about 500 mM, from about
30 mM to about 100 mM, from about 30 mM to abo ut 70 mM, from about 30 mM to about 50 mM, etc.).
[162] As indicated, one or more divalent cationic salts (e .g., MnCl 2 , MgCl 2 , MgSO 4 , CaCl 2 , etc.) may be included in compositions of the inventi on. In many instances, salts used in compositions of the invention will dissociate in solu tion to generate at least one species which is monovalent (e.g., Mg ++ , Mn ++ , Ca ++ , etc.). When included in compositions of the invention, salts will often be present either individ ually or in a combined concentration of from about 0.5 mM to about 500 mM (e.g., about 1 mM, about 2 mM, about 3 mM, about 4 mM, about 5 mM, about 6 mM, about 7 mM, about 8 mM, about 9 mM, about 10 mM, about 12 mM, about 15 mM, about 17 mM, about 20 mM, abo ut 22 mM, about 23 mM, about 24 mM, about 25 mM, about 27 mM, about 30 mM, about 35 mM, about 40 mM, about 45 mM, about 50 mM, about 55 mM, about 60 mM, about 64 m M, about 65 mM, about 70 mM, about 75 mM, about 80 mM, about 85 mM, about 90 m M, about 95 mM, about 100 mM, about 120 mM, about 140 mM, about 150 mM, about 17 5 mM, about 200 mM, about 225 mM, about 250 mM, about 275 mM, about 300 mM, abou t 325 mM, about 350 mM, about 375 mM, about 400 mM, from about 1 mM to about 50 0 mM, from about 5 mM to about 500 mM, from about 10 mM to about 500 mM, from ab out 20 mM to about 500 mM, from about 30 mM to about 500 mM, from about 40 mM to about 500 mM, from about 50 mM to about 500 mM, from about 60 mM to about 500 mM, f rom about 65 mM to about 500 mM, from about 75 mM to about 500 mM, from about 85 m M to about 500 mM, from about 90 mM to about 500 mM, from about 100 mM to about 50 0 mM, from about 125 mM to about 500 mM, from about 150 mM to about 500 mM, from a bout 200 mM to about 500 mM, from about 10 mM to about 100 mM, from about 10 mM to about 75 mM, from about 10 mM to about 50 mM, from about 20 mM to about 200 mM, fr om about 20 mM to about 150 mM, from about 20 mM to about 125 mM, from about 20 m M to about 100 mM, from about 20 mM to about 80 mM, from about 20 mM to about 75 mM, from about 20 mM to about 60 mM, from about 20 mM to about 50 mM, from about 3 0 mM to about 500 mM, from about 30 mM to about 100 mM, from about 30 mM to about 70 mM, from about 30 mM to about 50 mM, etc.).
[163] When included in compositions of the invention, reduc ing agents (e.g., dithiothreitol, β‐mercaptoethanol, etc.) will often be present eith er individually or in a combined concentration of from about 0.1 mM to about 50 mM (e.g., about 0.2 mM, about 0.3 mM,
about 0.5 mM, about 0.7 mM, about 0.9 mM, about 1 mM, about 2 mM, about 3 mM, about 4 mM, about 5 mM, about 6 mM, about 10 mM, about 12 mM, about 15 mM, about 17 mM, about 20 mM, about 22 mM, about 23 mM, about 24 m M, about 25 mM, about 27 mM, about 30 mM, about 35 mM, about 40 mM, about 45 m M, about 50 mM, from about 0.1 mM to about 50 mM, from about 0.5 mM to about 50 mM, from about 1 mM to about 50 mM, from about 2 mM to about 50 mM, from about 3 mM to about 50 mM, from about 0.5 mM to about 20 mM, from about 0.5 mM to about 10 mM, from about 0.5 mM to about 5 mM, from about 0.5 mM to about 2.5 mM, from about 1 m M to about 20 mM, from about 1 mM to about 10 mM, from about 1 mM to about 5 mM, f rom about 1 mM to about 3.4 mM, from about 0.5 mM to about 3.0 mM, from about 1 mM to about 3.0 mM, from about 1.5 mM to about 3.0 mM, from about 2 mM to about 3.0 mM, fr om about 0.5 mM to about 2.5 mM, from about 1 mM to about 2.5 mM, from about 1.5 m M to about 2.5 mM, from about 2 mM to about 3.0 mM, from about 2.5 mM to about 3.0 m M, from about 0.5 mM to about 2 mM, from about 0.5 mM to about 1.5 mM, from about 0.5 mM to about 1.1 mM, from about 5.0 mM to about 10 mM, from about 5.0 mM to about 15 mM, from about 5.0 mM to about 20 mM, from about 10 mM to about 15 mM, from about 1 0 mM to about 20 mM, etc.).
[164] Compositions of the invention may also contain one o r more ionic or non‐ionic detergents (e.g., TRITON X‐100™, NONIDET P40™, T ween 20, sodium dodecyl sulphate, etc.). When included in compositions of the invention, deter gents will often be present either individually or in a combined concentration of from about 0.001% to about 5.0% (e.g., about 0.001%, about 0.002%, about 0.003%, about 0.004%, abo ut 0.005%, about 0.006%, about 0.007%, about 0.008%, about 0.009%, about 0.01%, abou t 0.02%,about 0.05%, about 0.1, about 0.5%, about 1%, about 2%, about 5%, from abou t 0.001% to about 5.0%, from about 0.001% to about 4.0%, from about 0.001% to about 3. 0%, from about 0.001% to about 2.0%, from about 0.001% to about 1.0%, from about 0.005% to about 5.0%, from about 0.01% to about 3.0%, from about 0.01% to about 2.0%, from ab out 0.01% to about 1.0%, from about 0.1% to about 5.0%, from about 0.1% to about 4.0%, from about 0.1% to about 3.0%, from about 0.1% to about 2.0%, from about 0.1% to about 1.0%, from about 0.1% to about 0.5%, etc.). For example, compositions of the invention may contain Tween 20, NP‐40 and/or TRITON X100™ at a concentration of from about 0.01 % to about 2.0%, from about 0.03% to about 1.0%, from about 0.04% to about 1.0%, from ab out 0.05% to about 0.5%, from about 0.04% to about 0.6%, from about 0.04% to about 0.3% , etc.
[165] Other additives capable of facilitating or enhancing reverse transcription, amplification, or a combination of both reactions (e. g., agents for facilitating or enhancing RT‐PCR), other than those disclosed herein, are kno wn in the art. In accordance with the present compositions and methods, one or more of the se additives can be incorporated in the present compositions to optimize the generation a nd replication of nucleic acids from a ribonucleic acid or deoxyribonucleic acid templates. A dditives can be organic or inorganic compounds. Some additives useful in the present compo sitions, methods and kits include polypeptides as well as nonpolypeptide additives. Such additives can include, for example, RNase inhibitor protein (RIP), uracil DNA glycosylase (UDG), lectins, E. coli single‐stranded binding (SSB) protein, tRNA, rRNA, 7‐deaza‐2‐deox yguanosine (dC7GTP), sulfur‐containing compounds, acetate‐containing compounds, dimethylsulfox ide (DMSO), ribonuclease inhibitor (e.g., Rnase OUT™) formamide, betaine, tet ramethylammonium chloride ( TMAC), polyethylene glycol (PEG), ectoine, sodium azide, kath on, and polyols, to name just a few. Those of ordinary skill in the art will be able to identify additional additives for use in accordance with the present compositions, methods and kits.
[166] Compositions of the invention may also contain one o r more primers. In some embodiments, compositions of the invention comprise ol igo(dT) primers. These primers are typically ~20 bases in length, and anneal to the po lyA tails of mRNA. By targeting the mRNA fraction, the complexity of the resultant cDNA popula tion is dramatically reduced, since rRNA and tRNA species will not serve as templates in the reaction. The drawback of using oligo(dT) primers is that the resultant cDNA population will h ave a 3' bias, thus compromising the effectiveness of PCR primers targeting the 5' ends o f transcripts. In addition, due to the 3' bias, fragmented samples lacking a polyA tail will n ot be reverse transcribed.
[167] In other embodiments, compositions of the invention c omprise random primers. In some embodiments, the random primers are a random mi xture of 4 bases of a specified oligo length. Random hexamer mixes, for example, can be us ed. Each of the random primers can anneal anywhere the complementary sequence exists with in a given RNA molecule (including rRNA, tRNA, mRNA, and any fragments of these species ). Reverse transcription using random primers overcomes concerns about RNA secondary structu re, and RNA fragments, which are common headaches when using oligo(dT) primers.
[168] In some other embodiments, compositions of the invent ion comprise locked nucleic acid (LNA) primers. The incorporation of LNA into oligonucleotide primers has been shown
to increase template binding strength and specifici ty for DNA amplification. See, e.g., Ballantyne, K. N. , et al., Genomics. 2008 Mar;91(3) :301‐5.doi: 10.1016/j.ygeno.2007.10.016. LNA primers bind to polyA sequences with a higher m elting temperature (Tm) than those that do not comprise LNA.
[169] In other embodiments, compositions of the invention c omprise sequence‐specific (or gene‐specific) primers. Sequence specific primers typ ically offer the greatest specificity and have been shown to be the most consistent of the p rimer options for reverse transcription. However, they do not offer the flexibility of oligo( dT) and random primers, meaning that a new cDNA synthesis reaction must be performed for ea ch gene to be studied. This can sometimes makes sequence‐specific primers less than optimal for processing limiting tissue or cell samples. In some embodiments, a mixture of different types of primers (e.g., oligo(dT), random, LNA and/or sequence‐specific prime rs are used.
[170] Compositions of the invention may also comprise one or more hot start components. Hot‐start is a common technique used to reduce non specific amplification due to assembly of nucleic acid synthesis reactions at room temperature. At lower temperatures,
oligonucleotide primers can anneal to template sequenc es that are not perfectly
complementary. Oftentimes, at these low temperatures e nzymes such as reverse
transcriptases can extend misannealed primers. This ne wly synthesized region then acts as a template for primer extension and synthesis of undesi red nucleic acid synthesis products. However, if the reaction temperature is elevated (e.g ., to temperatures >60°C) before polymerization begins, the stringency of primer anneal ing is increased, and production of undesired nucleic acid synthesis products can be avoi ded or reduced.
[171] The inclusion of hot start components in nucleic aci d synthesis reactions can also reduce the amount of primer‐dimer synthesized by in creasing the stringency of primer annealing. At lower temperatures, oligonucleotide prime rs can anneal to each other via regions of complementarity to form hairpins, for exam ple, and the reverse transcriptase can extend the annealed primers to produce primer dimers. The formation of nonspecific products and primer‐dimers can compete for reagent availability for synthesis of the desired product. Thus, hot start techniques can improve the yield of specific nucleic acid synthesis products.
[172] In some embodiments, hot start reactions are assemble d on ice or at room
temperature, with omission of a critical component un til the reaction is heated to about
60°C, at which point the missing reagent is added. This omission prevents the reverse transcriptase from extending primers until the critica l component is added at the higher temperature where primer annealing is more stringent.
[173] In some other embodiments, the reverse transcriptase is reversibly inactivated or physically separated from one or more critical compon ents in the reaction. For example, magnesium can be sequestered in a wax bead, which m elts as the reaction is heated, releasing the component only at higher temperatures ( see, e.g., Carothers et al. 1989; Krishnan et al. 1991; Clark, 1988). The reverse tran scriptase can also be kept in an inactive state by binding to an oligonucleotide, also known a s an aptamer (see, e.g., Lin and Jayasena, 1997; Dang and Jayasena, 1996) or an antibody (see, e.g., Scalice et al. 1994; Sharkey et al. 1994). This bond can then be disrupted at a higher temperature, releasing the functional reverse transcriptase.
[174] In yet other embodiments, the reverse transcriptase c an be maintained in an inactive state through chemical modification (see, e.g., Morett i, T. et al 1998). In some
embodiments, the chemical modification is reversible. Thus, in some embodiments, the reverse transcriptase is chemically modified such that it is in an inactive state at a lower temperature (e.g., less than about 55°C) and is ful ly functional/active at an elevated temperature (e.g., greater than about 55°C).
[175] Compositions of the invention may also contain one o r more DNA polymerase inhibitors (e.g., Actinomycin D, etc.). When included in compositions of the invention, such inhibitors will often be present either individually or in a combined concentration of from about 0.1 μg/ml to about 100 μg/ml (e.g., about 0 .1 μg/ml, about 0.2 μg/ml, about 0.3 μg/ml, about 0.4 μg/ml, about 0.5 μg/ml, about 0. 6 μg/ml, about 0.7 μg/ml, about 0.8 μg/ml, about 0.9 μg/ml, about 1.0 μg/ml, about 1.1 μg/ml , about 1.3 μg/ml, about 1.5 μg/ml, about 1.7 μg/ml, about 2.0 μg/ml, about 2.5 μg/ml, abou t 3.5 μg/ml, about 5.0 μg/ml, about 7.5 μg/ml, about 10 μg/ml, about 15 μg/ml, about 20 μg/ml, about 25 μg/ml, about 30 μg/ml, about 35 μg/ml, about 40 μg/ml, about 50 μg/ml, about 60 μg/ml, about 70 μg/ml, about 80 μg/ml, about 90 μg/ml, about 100 μg/ml, from abou t 0.5 μg/ml to about 30 μg/ml, from about 0.75 μg/ml to about 30 μg/ml, from about 1. 0 μg/ml to about 30 μg/ml, from about 2.0 μg/ml to about 30 μg/ml, from about 3.0 μg/m l to about 30 μg/ml, from about 4.0 μg/ml to about 30 μg/ml, from about 5.0 μg/ml to about 30 μg/ml, from about 7.5 μg/ml to about 30 μg/ml, from about 10 μg/ml to about 30 μg/ml, from about 15 μg/ml to about 30 μg/ml,
from about 0.5 μg/ml to about 20 μg/ml, from a bout 0.5 μg/ml to about 10 μg/ml, from about 0.5 μg/ml to about 5 μg/ml, from about 0.5 μg/ml to about 2 μg/ml, from about 0.5 μg/ml to about 1 μg/ml, from about 1 μg/ml to a bout 10 μg/ml, from about 1 μg/ml to about 5 μg/ml, from about 1 μg/ml to about 2 μg/ml, f rom about 1 μg/ml to about 100 μg/ml, from about 10 μg/ml to about 100 μg/ml, from about 20 μg/ml to about 100 μg/ml, from about 40 μg/ml to about 100 μg/ml, from about 30 μg/ml to about 80 μg/ml, from about 30 μg/ml to about 70 μg/ml, from about 40 μg/ml to about 60 μg/ml, from about 40 μg/ml to about 70 μg/ml, from about 40 μg/ml to about 80 μg/ml, et c.).
[176] In many instances, nucleotides (e.g., dNTPs, such as dGTP, dATP, dCTP, dTTP, etc.) will be present in reaction mixtures of the invention. Ty pically, individually nucleotides will be present in concentrations of from about 0.05 mM to about 50 mM (e.g., about 0.07 mM, about 0.1 mM, about 0.15 mM, about 0.18 mM, about 0.2 mM, about 0.3 mM, about 0.5 mM, about 0.7 mM, about 0.9 mM, about 1 mM, about 2 mM, about 3 mM, about 4 mM, about 5 mM, about 6 mM, about 10 mM, about 12 mM, about 15 mM, about 17 mM, about 20 mM, about 22 mM, about 23 mM, about 24 mM, abo ut 25 mM, about 27 mM, about 30 mM, about 35 mM, about 40 mM, about 45 mM, about 50 mM, from about 0.1 mM to about 50 mM, from about 0.5 mM to about 50 mM, from abo ut 1 mM to about 50 mM, from about 2 mM to about 50 mM, from about 3 mM to about 50 mM, from about 0.5 mM to about 20 mM, from about 0.5 mM to about 10 mM, from about 0.5 mM to about 5 mM, from about 0.5 mM to about 2.5 mM, from about 1 mM to about 20 mM, from about 1 mM to about 10 mM, from about 1 mM to about 5 mM, from about 1 mM to about 3.4 mM, from about 0.5 mM to about 3.0 mM, from about 1 mM to about 3.0 mM, from about 1.5 mM to about 3.0 mM, from about 2 mM to about 3.0 mM, from about 0 .5 mM to about 2.5 mM, from about 1 mM to about 2.5 mM, from about 1.5 mM to about 2. 5 mM, from about 2 mM to about 3.0 mM, from about 2.5 mM to about 3.0 mM, from about 0.5 mM to about 2 mM, from about 0.5 mM to about 1.5 mM, from about 0.5 mM to abou t 1.1 mM, from about 5.0 mM to about 10 mM, from about 5.0 mM to about 15 mM, from abo ut 5.0 mM to about 20 mM, from about 10 mM to about 15 mM, from about 10 mM to about 20 mM, etc.). The combined nucleotide concentration, when more than one nucleotid es is present, can be determined by adding the concentrations of the individual nucleotide s together. When more than one nucleotide is present in compositions of the inventio n, the individual nucleotides may not be
present in equimolar amounts. Thus, a composition may contain, for example, 1 mM dGTP, 1 mM dATP, 0.5 mM dCTP, and 1 mM dTTP.
[177] RNA will typically be present in compositions of the invention. In most instances, RNA will be added to the composition shortly prior to r everse transcription. Thus, compositions may be provided without RNA. This will typically be the case when compositions are provided in kits. RNA, when present in compositions will often be present in a concentration of 1 picogram to 100 μg/20 μl reaction mixture (e .g., about 1 picogram/20 μl, about 10 picograms/20 μl, about 50 picograms/20 μl, about 10 0 picograms/20 μl, about 200 picograms/20 μl, about 10 picograms/20 μl, about 50 0 picograms/20 μl, about 800 picograms/20 μl, about 1.0 nanogram/20 μl, about 5. 0 nanograms/20 μl, about 10 nanograms/20 μl, about 25 nanograms/20 μl, about 50 nanograms/20 μl, about 75 nanograms/20 μl, about 100 nanograms/20 μl, about 1 50 nanograms/20 μl, about 250 nanograms/20 μl, about 400 nanograms/20 μl, about 5 00 nanograms/20 μl, about 750 nanograms/20 μl, about 1.0 μg/20 about 5.0 μg/20 μl, about 10 μg/20 μl, about 20 μg/20 μl, about 30 μg/20 μl, about 40 μg/20 μl, about 50 μg/20 μl, about 70 μg/20 μl, about 85 μg/20 μl, about 100 μg/20 μl, from about 10 picograms/2 0 μl to about 100 μg/20 μl, from about 10 picograms/20 μl to about 100 μg/20 μl, from about 100 picograms/20 μl to about 100 μg/20 μl, from about 1.0 nanograms/20 μl to about 100 g/20 μl, from about 100 nanograms/20 μl to about 100 μg/20 μl, from about 10 picograms/20 μl to about 10 μg/20 μl, from about 10 picograms/20 μl to about 5 μg/20 μl, from about 100 nanograms/20 μl to about 5 μg/20 μl, from about 1 μg/20 μl to about 10 μg/20 μl, fr om about 1 μg/20 μl to about 5 μg/20 μl, from about 100 nanograms/20 μl to about 1 μg/20 μl, f rom about 500 nanograms/20 μl to about 5 μg/20 μl, etc.). As one skilled in the art would recognize, different reverse transcription reactions may be performed in volumes other than 20 μl. In such instances, the total amount of RNA present will vary with the volume used. Thus , the above amounts are provided as examples of the amount of RNA/20 μl of composition.
[178] Mutant reverse transcriptases of the invention when p resent in compositions as described herein (storage compositions and/or reaction mixtures), can be present in a concentration which results in about 0.01 to about 1 ,000 units of reverse transcriptase activity/μl (e.g., about 0.01 unit/μl, about 0.05 u nit/μl, about 0.1 unit/μl, about 0.2 unit/μl, about 0.3 unit/μl, about 0.4 unit/μl, about 0.5 un it/μl, about 0.7 unit/μl, about 1.0 unit/μl, about 1.5 unit/μl, about 2.0 unit/μl, about 2.5 un it/μl, about 5.0 unit/μl, about 7.5 unit/μl,
about 10 unit/μl, about 20 unit/μl, about 25 un it/μl, about 50 unit/μl, about 100 unit/μl, about 150 unit/μl, about 200 unit/μl, about 250 un it/μl, about 350 unit/μl, about 500 unit/μl, about 750 unit/μl, about 1,000 unit/μl, from about 0.1 unit/μl to about 1,000 unit/μl, from about 0.2 unit/μl to about 1,000 unit/μl, from abo ut 1.0 unit/μl to about 1,000 unit/μl, from about 5.0 unit/μl to about 1,000 unit/μl, from abo ut 10 unit/μl to about 1,000 unit/μl, from about 20 unit/μl to about 1,000 unit/μl, from abou t 50 unit/μl to about 1,000 unit/μl, from about 100 unit/μl to about 1,000 unit/μl, from abo ut 200 unit/μl to about 1,000 unit/μl, from about 400 unit/μl to about 1,000 unit/μl, from abo ut 500 unit/μl to about 1,000 unit/μl, from about 0.1 unit/μl to about 300 unit/μl, from about 0.1 unit/μl to about 200 unit/μl, from about 0.1 unit/μl to about 100 unit/μl, from about 0.1 unit/μl to about 50 unit/μl, from about 0.1 unit/μl to about 10 unit/μl, from about 0.1 u nit/μl to about 5.0 unit/μl, from about 0.1 unit/μl to about 1.0 unit/μl, from about 0.2 unit/ μl to about 0.5 unit/μl, etc.
[179] Compositions of the invention may be prepared as con centrated solutions (e.g., 5× solutions) which are diluted to a working concentrati on for final use. With respect to a 5× composition, a 5:1 dilution is required to bring suc h a 5× solution to a working concentration. Compositions of the invention may be prepared, for e xamples, as a 2×, a 3×, a 4×, a 5×, a 6×, a 7×, a 8×, a 9×, a 10×, etc. solutions. One limitation on the fold concentration of such solutions is that, when compounds reach particular co ncentrations in solution, precipitation can occur. Thus, concentrated compositions will genera lly be prepared such that the concentrations of the various components are low enou gh so that precipitation of buffer components will not occur. As one skilled in the ar t would recognize, the upper limit of concentration which is feasible for each solution wil l vary with the particular solution and the components present.
[180] In many instances, compositions of the invention will be provided in sterile form. Sterilization may be performed on the individual comp onents of compositions prior to mixing or on compositions after they are prepared. Steriliza tion of such solutions may be performed by any suitable means including autoclaving or ultraf iltration.
Methods of Using Reverse Transcriptases
[181] The reverse transcriptases of the invention may be u sed to make nucleic acid
molecules from one or more templates. Such methods c an comprise mixing one or more
nucleic acid templates (e.g., DNA or RNA, such as non‐coding RNA (ncRNA), messenger RNA (mRNA), micro RNA (miRNA), and small interfering RNA (siRNA) molecules) with one or more of the reverse transcriptases of the invention and i ncubating the mixture under conditions sufficient to make one or more nucleic acid molecule s complementary to all or a portion of the one or more nucleic acid templates.
[182] The invention also concerns nucleic acid molecules pr oduced by such methods (which may be full‐length cDNA molecules), vectors (particu larly expression vectors) comprising these nucleic acid molecules and host cells comprisin g these vectors and nucleic acid molecules.
[183] Other methods of cDNA synthesis which may advantageou sly use the present invention will be readily apparent to one of ordinar y skill in the art.
[184] The invention also provides methods for the amplifica tion of one or more nucleic acid molecules comprising mixing one or more nucleic acid templates with one of the reverse transcriptases of the invention, and incubating the m ixture under conditions sufficient to amplify one or more nucleic acid molecules complement ary to all or a portion of the one or more nucleic acid templates. Such amplification method s may further comprise the use of one or more DNA polymerases and may be employed as in standard reverse transcription‐ polymerase chain reaction (RT‐PCR) reactions.
[185] Nucleic acid amplification methods according to this aspect of the invention may be one‐step (e.g., one‐step RT‐PCR) or two‐step ( e.g., two‐step RT‐PCR) reactions. According to the invention, one‐step RT‐PCR type reactions may be accomplished in one tube thereby lowering the possibility of contamination. Such one‐ step reactions comprise (a) mixing a nucleic acid template (e.g., mRNA) with one or more reverse transcriptases of the present invention and with one or more DNA polymerases and (b) incubating the mixture under conditions sufficient to amplify a nucleic acid molec ule complementary to all or a portion of the template. Such amplification may be accomplished by the reverse transcriptase activity alone or in combination with the DNA polymerase acti vity. Two‐step RT‐PCR reactions may be accomplished in two separate steps. Such a method comprises (a) mixing a nucleic acid template (e.g., mRNA) with a reverse transcriptase of the present invention, (b) incubating the mixture under conditions sufficient to make a nu cleic acid molecule (e.g., a DNA molecule) complementary to all or a portion of the template, (c) mixing the nucleic acid molecule with one or more DNA polymerases and (d) i ncubating the mixture of step (c)
under conditions sufficient to amplify the nucleic acid molecule. For amplification of long nucleic acid molecules (i.e., greater than about 3‐ 5 kb in length), a combination of DNA polymerases may be used, such as one DNA polymerase having 3 exonuclease activity and another DNA polymerase being substantially reduced in 3 exonuclease activity.
[186] Amplification methods which may be used in accordance with the present invention include PCR (see, e.g., U.S. Pat. Nos. 4,683,195 and 4,683,202), Isothermal Amplification (using one or more RNA polymerases (see, e.g., PCT Publication No. WO 2006/081222), Strand Displacement Amplification (SDA; see, e.g., U.S . Pat. No. 5,455,166; EP 0 684 315), and Nucleic Acid Sequence‐Based Amplification (NASBA; see , e.g., U.S. Pat. No. 5,409,818; EP 0 329 822), as well as more complex PCR‐based nuclei c acid fingerprinting techniques such as Random Amplified Polymorphic DNA (RAPD) analysis (see, e.g., Williams, J. G. K., et al., Nucl. Acids Res. 18(22):6531‐6535, 1990), Arbitrarily Prime d PCR (AP‐PCR; see, e.g., Welsh, J., and McClelland, M., Nucl. Acids Res. 18(24):7213‐7218, 1 990), DNA Amplification Fingerprinting (DAF; see, e.g., Caetano‐Anollés et al., Bio/Techno logy 9:553‐557, 1991), microsatellite PCR or Directed Amplification of Minisatellite‐region DNA (DAVID; see, e.g., Heath, D. D., et al. Nucl. Acids Res. 21(24): 5782‐5785 (1993), and Ampl ification Fragment Length Polymorphism (AFLP) analysis (see, e.g., EP 0 534 858; Vos, P., et al. Nucl. Acids Res. 23(21):4407‐4414 (1995); Lin, J. J., and Kuo, J. FOCUS 17(2):66‐70 (1995). Nucleic acid sequencing techniques which may employ the present compositions include did eoxy sequencing methods such as those disclosed in U.S. Pat. Nos. 4,962,022 and 5,49 8,523. In some embodiments, the invention may be used in methods of amplifying or s equencing a nucleic acid molecule comprising one or more polymerase chain reactions (PC Rs), such as any of the PCR‐based methods described above.
[187] The invention also concerns methods for the sequencin g of one or more nucleic acid molecules comprising (a) mixing one or more nucleic acid molecules to be sequenced with one or more primer nucleic acid molecules, one or m ore reverse transcriptases of the invention, one or more nucleotides and one or more terminating agents; (b) incubating the mixture under conditions sufficient to synthesize a p opulation of nucleic acid molecules complementary to all or a portion of the one or mo re nucleic acid molecules to be sequenced; and (c) separating the population of nucle ic acid molecules to determine the nucleotide sequence of all or a portion of the one or more nucleic acid molecules to be sequenced.
[188] Nucleic acid sequencing methods according to this asp ect of the invention can comprise both cycle sequencing (sequencing in combinat ion with amplification) and standard sequencing reactions. The sequencing method of the in vention thus comprises (a) mixing a nucleic acid molecule to be sequenced with one or m ore primers, one or more reverse transcriptase of the invention, one or more nucleotid es and one or more terminating agents, (b) incubating the mixture under conditions sufficient to synthesize a population of nucleic acid molecules complementary to all or a portion of the molecule to be sequenced, and (c) separating the population to determine the nucleotide sequence of all or a portion of the molecule to be sequenced. According to the invention, one or more DNA polymerases (preferably thermostable DNA polymerases) can be used in combination with or separate from the reverse transcriptases of the invention.
[189] In accordance with the invention, cDNA molecules (sin gle‐stranded or double‐ stranded) can be prepared from a variety of nucleic acid template molecules using the novel mutant reverse transcriptases provided herein. Preferre d nucleic acid molecules for use in the present invention include single‐stranded or dou ble‐stranded DNA and RNA molecules, as well as double‐stranded DNA:RNA hybrids. More pr eferred nucleic acid molecules include messenger RNA (mRNA), transfer RNA (tRNA) and ribosom al RNA (rRNA) molecules, although mRNA molecules are the preferred template according t o the invention. In certain embodiments gene‐specific primers can be used. In c ertain other embodiments in which at least some of the mutant reverse transcriptases provi ded herein are well‐suited, oligo dT primers are used. These dT primers can be LNA prime rs in some embodiments. Furthermore, in illustrative examples, the templates for such reac tions can be mRNA.
[190] The nucleic acid molecules that are used to prepare cDNA molecules according to the methods of the present invention may be prepared syn thetically according to standard organic chemical synthesis methods that will be famil iar to one of ordinary skill. More preferably, the nucleic acid molecules may be obtaine d from natural sources, such as a variety of cells, tissues, organs or organisms. Cells that may be used as sources of nucleic acid molecules may be prokaryotic (bacterial cells, includi ng but not limited to those of species of the genera Escherichia, Bacillus, Serratia, Salmonella, Staphylococcus, Streptococcus, Clostridium, Chlamydia, Neisseria, Treponema, Mycoplasma , Borrelia, Legionella,
Pseudomonas, Mycobacterium, Helicobacter, Erwinia, Agrob acterium, Rhizobium,
Xanthomonas and Streptomyces) or eukaryotic (including fungi (especially yeasts), plants,
protozoans and other parasites, and animals includi ng insects (particularly Drosophila spp. cells), nematodes (particularly Caenorhabditis elegans cells), and mammals (particularly human cells)).
[191] Mammalian somatic cells that may be used as sources of nucleic acids include blood cells (reticulocytes and leukocytes), endothelial cells , epithelial cells, neuronal cells (from the central or peripheral nervous systems), muscle cells (including myocytes and myoblasts from skeletal, smooth or cardiac muscle), connective tissue cells (including fibroblasts, adipocytes, chondrocytes, chondroblasts, osteocytes and osteoblasts) and other stromal cells (e.g., macrophages, dendritic cells, Schwann cells). Mammalian germ cells (spermatocytes and oocytes) may also be used as sources of nucleic aci ds for use in the invention, as may the progenitors, precursors and stem cells that give rise to the above somatic and germ cells. Also suitable for use as nucleic acid sources are m ammalian tissues or organs such as those derived from brain, kidney, liver, pancreas, blood, b one marrow, muscle, nervous, skin, genitourinary, circulatory, lymphoid, gastrointestinal a nd connective tissue sources, as well as those derived from a mammalian (including human) embryo or fetus.
[192] Any of the above prokaryotic or eukaryotic cells, ti ssues and organs may be normal, diseased, transformed, established, progenitors, precurs ors, fetal or embryonic. Diseased cells may, for example, include those involved in in fectious diseases (caused by bacteria, fungi or yeast, viruses (including AIDS, HIV, HTLV, herpes, hepatitis and the like) or parasites), in genetic or biochemical pathologies (e.g., cystic f ibrosis, hemophilia, Alzheimer's disease, muscular dystrophy or multiple sclerosis) or in cance rous processes. Transformed or established animal cell lines may include, for exampl e, COS cells, CHO cells, VERO cells, BHK cells, HeLa cells, HepG2 cells, K562 cells, 293 cell s, L929 cells, F9 cells, and the like. Other cells, cell lines, tissues, organs and organisms suit able as sources of nucleic acids for use in the present invention will be apparent to one of or dinary skill in the art.
[193] In some embodiments, a composition can comprise genom ic nucleic acid. In some embodiments, a composition can comprise maternal nucle ic acid, fetal nucleic acid or a mixture of maternal and fetal nucleic acids. In some embodiments, a composition can comprise fragments of genomic nucleic acids. In some embodiments a composition can comprise nucleic acids derived from a virus, bacteria , yeast, fungus, mammal or mixture thereof. A nucleic acid sample may be derived from one or more sources. A sample may be collected from an organism, mineral or geological sit e (e.g., soil, rock, mineral deposit, fossil),
or forensic site (e.g., crime scene, contraband or suspected contraband), for example. Thus, a source may be environmental, such as geological, agri cultural, combat theater or soil sources, for example. A source also may be from any type of organism such as any plant, fungus, protistan, moneran, virus or animal, including but not limited, human, non‐human, mammal, reptile, cattle, cat, dog, goat, swine, pig, monkey, ape, gorilla, bull, cow, bear, horse, sheep, poultry, mouse, rat, fish, dolphin, wha le, and shark, or any animal or organism that may have a detectable nucleic acids. Sources al so can refer to different parts of an organism such as internal parts, external parts, livi ng or nonliving cells, tissue, fluid and the like. A sample therefore may be a "biological sample ," which refers to any material obtained from a living source or formerly‐living source, for example, an animal such as a human or other mammal, a plant, a bacterium, a fungus, a pro tist or a virus. A source can be in any form, including, without limitation, a solid material such as a tissue, cells, a cell pellet, a cell extract, or a biopsy, or a biological fluid such as urine, blood, saliva, amniotic fluid, exudate from a region of infection or inflammation, or a mo uth wash containing buccal cells, hair, cerebral spinal fluid and synovial fluid and organs. A sample also may be isolated at a different time point as compared to another sample, where each of the samples are from the same or a different source. A nucleic acid may be from a nucleic acid library, such as a cDNA or RNA library, for example. A nucleic acid may be a result of nucleic acid purification or isolation and/or amplification of nucleic acid molecul es from the sample. Nucleic acid provided for sequence analysis processes described her ein may contain nucleic acid from one sample or from two or more samples (e.g., from 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13 , 14, 15, 16, 17, 18, 19, 20, 25, 50, 75, 100, 200, 300, 400, 500, 600, 700, 800, 900 or 1000 or more samples). Nucleic acids may be treated in a va riety of manners. For example, a nucleic acid may be reduced in size (e.g., sheared, digested by nuclease or restriction enzyme, de‐ phosphorylated, de‐ methylated), increased in size ( e.g., phosphorylated, reacted with a methylation‐specific reagent, attached to a detectabl e label), treated with inhibitors of nucleic acid cleavage and the like.
[194] Nucleic acids may be provided for conducting methods described herein without processing, in certain embodiments. In some embodiment s, nucleic acid is provided for conducting methods described herein after processing. For example, a nucleic acid may be extracted, isolated, purified or amplified from a sam ple. The term "isolated" as used herein refers to nucleic acid removed from its original env ironment (e.g., the natural environment if
it is naturally occurring, or a host cell if exp ressed exogenously), and thus is altered "by the hand of man" from its original environment. An isola ted nucleic acid generally is provided with fewer non‐nucleic acid components (e.g., protei n, lipid) than the amount of
components present in a source sample. A composition comprising isolated nucleic acid can be substantially isolated (e.g., about 90%, 91 %, 92 %, 93%, 94%, 95%, 96%, 97%, 98%, 99% or greater than 99% free of non‐nucleic acid component s). The term "purified" as used herein refers to nucleic acid provided that contains fewer nucleic acid species than in the sample source from which the nucleic acid is derived. A co mposition comprising nucleic acid may be substantially purified (e.g., about 90%, 91 %, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or greater than 99% free of other nucleic acid species) .
[195] Nucleic acids may be processed by a method that gen erates nucleic acid fragments, in certain embodiments, before providing nucleic acid for a process described herein. In some embodiments, nucleic acid subjected to fragmentation o r cleavage may have a nominal, average or mean length of about 5 to about 10,000 base pairs, about 100 to about 1 ,00 base pairs, about 100 to about 500 base pairs, or about 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 200, 300, 400, 5 00, 600, 700, 800, 900, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000 or 10000 base pa irs. Fragments can be generated by any suitable method known in the art, and the average, mean or nominal length of nucleic acid fragments can be controlled by selecting an appropria te fragment‐generating procedure. In certain embodiments, nucleic acid of a relatively sho rter length can be utilized to analyze sequences that contain little sequence variation and/o r contain relatively large amounts of known nucleotide sequence information. In some embodim ents, nucleic acid of a relatively longer length can be utilized to analyze sequences t hat contain greater sequence variation and/or contain relatively small amounts of unknown nu cleotide sequence information. As used herein, the term "target nucleic acid" or "targ et nucleic acid species" refers to any nucleic acid species of interest in a sample. A tar get nucleic acid includes, without limitation, (i) a particular allele amongst two or more possible alleles, and (ii) a nucleic acid having, or not having, a particular mutation, nucleotide substitu tion, sequence variation, repeat sequence, marker or distinguishing sequence.
[196] Once the starting cells, tissues, organs or other sa mples are obtained, nucleic acid molecules (such as mRNA) may be isolated therefrom b y methods that are well‐known in the art (See, e.g., Maniatis, T., et al., Cell 15:687‐ 701 (1978); Okayama, H., and Berg, P., Mol. Cell.
Biol. 2:161‐170 (1982); Gubler, U., and Hoffman, B. J., Gene 25:263‐269 (1983)). The nucleic acid molecules thus isolated may then be used to pr epare cDNA molecules and cDNA libraries in accordance with the present invention.
Kits
[197] In another embodiment, the present invention may be assembled into kits, which may be used in reverse transcription or amplification of a nucleic acid molecule, or into kits for use in sequencing of a nucleic acid molecule. K its according to this aspect of the invention comprise a carrier means, such as a box, carton, tu be or the like, having in close confinement therein one or more container means, such as vials, tubes, ampoules, bottles and the like, wherein a first container means contains one or more polypeptides of the present invention having reverse transcriptase activity. When more than one polypeptide having reverse transcriptase activity is used, they may be in a si ngle container as mixtures of two or more polypeptides, or in separate containers. The kits of the invention can also comprise (in the same or separate containers) one or more DNA polymer ases, a suitable buffer, one or more nucleotides and/or one or more primers. The kits of the invention can also comprise one or more hosts or cells including those that are compete nt to take up nucleic acids (e.g., DNA molecules including vectors). Preferred hosts may incl ude chemically competent or electrocompetent bacteria such as E. coli (including DH5, DH5α, DH10B, HB101, Top 10, and other K‐12 strains as well as E. coli B and E. coli W strains).
[198] In a specific aspect of the invention, the kits of the invention (e.g., reverse
transcription and amplification kits) can include one or more components (in mixtures or separately) including one or more polypeptides having reverse transcriptase activity of the invention, one or more nucleotides (one or more of which may be labeled, e.g., fluorescently labeled) used for synthesis of a nucleic acid molecu le, and/or one or more primers (e.g., oligo(dT) for reverse transcription). Such kits (inclu ding the reverse transcription and amplification kits) can further comprise one or more DNA polymerases. Sequencing kits of the invention may comprise one or more polypeptides having reverse transcriptase activity of the invention, and optionally one or more DNA po lymerases, one or more terminating agents (e.g., dideoxynucleoside triphosphate molecules) used for sequencing of a nucleic acid molecule, one or more nucleotides and/or one or more primers. Preferred polypeptides
having reverse transcriptase activity, DNA polymeras es, nucleotides, primers and other components suitable for use in the reverse transcript ion, amplification and sequencing kits of the invention include those described above. The kits encompassed by this aspect of the present invention may further comprise additional reag ents and compounds necessary for carrying out standard nucleic acid reverse transcripti on, amplification or sequencing protocols. Such polypeptides having reverse transcripta se activity of the invention, DNA polymerases, nucleotides, primers, and additional reage nts, components or compounds can be contained in one or more containers, and can be contained in such containers in a mixture of two or more of the above‐noted components or m ay be contained in the kits of the invention in separate containers. Such kits can also comprise instructions (e.g., for performing the methods of the invention such as for labeling nucleic acid molecules in accordance with the invention).
[199] In certain illustrative embodiments, the kits of the invention are prepared for
molecular diagnostics assays. The kits can be appro ved by a government regulatory agency that regulates the sale of diagnostics products for human diagnostics, animal diagnostics, environmental diagnostics and/or food safety. The reve rse transcriptases of the present invention can be provided in place of current revers e transcriptases in such kits.
Furthermore, the advantageous and surprising properties of the novel reverse transcriptases of the present invention make them particularly well suited for these applications.
[200] In some embodiments, the kits of the invention inclu de one or more components, including, but not limited to: an internal and/or ex ternal positive control, a set of
oligonucleotides for detection of the target gene (e. g., primer and/or probe), lysis buffer, uracil DNA glycosylase (UDG), a master mix, and a d etection dye.
[201] It will be readily apparent to one of ordinary skil l in the relevant arts that other suitable modifications and adaptations to the methods and applications described herein are obvious and may be made without departing from the scope of the invention or any embodiment thereof. Section headings provided herein a re for convenience only. Having now described the present invention in detail, the s ame will be more clearly understood by reference to the following examples, which are includ ed herewith for purposes of illustration only and are not intended to be limiting of the in vention.
EXAMPLES Example 1
Comparison of Thermostability and Processivity of Vari ous Reverse Transcriptases
[202] 2 µg of 0.24‐9.5 kb RNA Ladder (Invitrogen, Cat. No. 15620016) and 5 µM of 5’ labeled oligo(dT) 20 primer (Alexa‐647) was added to a final rea ction volume of 19 µL of 1X 1st strand cDNA synthesis buffer, pH 8.4 (Life Technologi es, Cat. No. Y02321) supplemented with 10 mM DTT, 500 µM of each dNTP (dATP, dTTP, dGTP and dCTP), and 2U RNaseOut
(Invitrogen, Cat. No. 10777‐019) and incubated on i ce. Reactions were then initiated by adding 1 µL of a reverse transcriptase (200U/µl) ( to a final volume 20 µL) followed by incubation at 60°C, 37°C, 42°C, or 50°C (as indi cated in Figure 2) for various lengths of time (i.e., 5 minutes, 15 minutes and 60 minutes). At th e end of each time point, the reactions were terminated by addition of 10 µl of alkaline l oading dye (300mM NaOH, 2mM EDTA, 20% glycerol, 10% saturated Thymol Blue) and visualized b y electrophoresis on a 1% alkaline agarose gel (30 mM NaOH, 2 mM EDTA pH 7.5) in buf fer (30 mM NaOH, 2 mM EDTA pH 7.5) for 2‐4 hours at 30 volts. The gel was then anal yzed by Molecular Dynamics Typhoon 8600 Variable Mode Imager (Harlow Scientific) using ImageQu ant software.
[203] As Figure 2 shows, reactions that include mutant M MLV RT “Mut D9” (SEQ ID NO:4), an exemplary mutant M‐MLV constructed using the tea chings herein, produced cDNAs up to 7.5 kb as early as 5 minutes after incubation and cDNAs up to 9.5 kb after only 15 minutes of incubation at 60°C. This is in contrast to reac tions comprising wild type M‐MLV RT incubated at 37°C which required up to 60 minutes to produce a comparable amount of 7.5 kb cDNAs. Similarly, 7.5 kb cDNAs were not detected in reactio ns comprising either SuperScript™ II (“SSII”) or SuperScript™ III (“SSIII”)RTs unt il more than 5 minutes of incubation at 42°C or 50°C, respectively. Another commercially available R T (“Q‐RT”) that was examined did not produce any similar cDNAs even after 60 minutes of incubation at 37°C. This demonstrates that mutant M‐MLV (“Mut D9”) RT was highly pro cessive and exhibited increased
thermostability, as well as thermoreactivity, in rever se transcription reactions performed at temperatures as high as 60°C.
Example 2
Mutant Reverse Transcriptase Stability at Low pH
[204] Comparison of wild type M‐MLV RT (Invitrogen™, Ca talog # 28025‐013) (“WT MMLV”) and an exemplary mutant M‐MLV RT (“Mut D9”) was performed to evaluate speed and length of cDNA synthesized at varying pH. These assays contained 0.5‐10 kb RNA ladder (Ambion®, Catalog # 15623‐200) and Alexa Fluor® 6 47 oligo(dT)20 and was performed with a standard pH 8.3 buffer (50 mM Tris‐HCl pH 8.3, 72 .5 mM KCl, and 3 mM MgCl2) or a pH 7.3 buffer (50 mM Tris‐HCl pH 7.3, 72.5 mM KCl, and 3 mM MgCl2). Reaction temperatures were 37 °C for wild type M‐MLV and 50 °C for Mut D9 and RT reactions were carried out for varying lengths of time (i.e., 10 minutes, 30 minute s or 60 minutes, as indicated in Figure 3). The first strand cDNAs produced were resolved by alkaline agarose gel electrophoresis and visualized using Molecular Dynamics Typhoon 8600 Varia ble Mode Imager (Harlow Scientific) set at Cy5 flourescent mode.
[205] As Figure 3 shows, at pH 8.3, Mut D9 reaches 4 kb by 10 minutes while wild type M‐ MLV reaches only 3 kb in the same amount of time. At pH 7.3, Mutant D9 can reach 4 kb in 30 minutes whereas wild type M‐MLV cannot produce cDNA over 3 kb even after 60 minute RT reaction time. Mut D9 is therefore more active t han wild type M‐MLV at a wider range of pH, producing more cDNA and longer cDNA at both pH 8.3 and pH 7.3, even while at a higher temperature than wild type M‐MLV.
Example 3
Mutant Reverse Transcriptase Thermostability
[206] The experiment described in Example 2 was also perfo rmed at 60 °C for varying lengths of time (i.e., 5 minutes, 10 minutes, 30 mi nutes or 60 minutes, as indicated in Figure 4) to evaluate thermostability of an exemplary mutant RT as described herein (“Mut D9”) compared to wild type M‐MLV (“WT MMLV”) and ot her commercially available RTs (“SSIII” and “C‐RT”). At this temperature, a standard ol igo(dT) 20 cannot anneal to the polyadenylated tail of the RNA targets because the melting temperat ure is around 50 °C. Instead an LNA™ oligo‐T20 (Exiqon Life Sciences) containing 50% LNA was utilized. Another difference in the
experiment is that reaction mix containing buffer, RNA targets, and primer were first heated to 60 °C prior to the addition of RT enzyme (“m anual hot start”). Manual hot start was performed to eliminate cDNA synthesis during reaction set up and temperature ramp up time. At pH 8.3 and 60 °C, all enzymes except Mut D9 are non‐functional. Mut D9 speed, cDNA yield, and cDNA length performance remains uncha nged at 60 °C (see Figure 4) compared to 50 °C (compare to Figure 3). Thus, Mut D9 is both thermostable and thermoreactive ‐ it can refold into an active enzy me after being heated to a higher temperature (thermostable) as well as synthesize cDNA at higher temperatures
(thermoreactive) (see, e.g., Figure 4).
Example 4
Evaluation of Reverse Transcription Sensitivity and Th ermostability
[207] For all reactions, 100, 50 or 10 ng per 20 µL re action of Hela RNA (Life Technologies, Cat. No. AM7852, Cervical Adenocarcinoma (Hela‐S3) T otal RNA) was incubated at the temperatures and times indicated below in: (1) the a bsence of primer, (2) in the presence of oligo(dT) 20 primer; (3) in the presence of LNA T20 prime r (Exiqon); and (4) in the presence of a gene specific primer (PolE 2.5 kb‐rev primer seq uence: GACCAGGTCCTGCAGGGTGAAGGC). Each reaction mixture contained the indicated amount of Hela RNA (as indicated in Figure 5), 1mM of each dNTP (dATP, dTTP, dGTP and dCTP) (Life Technologies, Cat. No. 10297018), 5 mM DTT (Life Technologies, Cat. No. Y00147), 1X Firs t strand buffer (Life Technologies, Cat. No. Y02321), 1 µM primer (1, 2, 3, or 4, as desc ribed above and indicated in Figure 5), 40 U RNaseOut (Life Technologies, Cat. No. 10777019) and 1 00 U of other commercially available mutant M‐MLV reverse transcriptase (“SSIII” and “M‐RT”), or an exemplary mutant M‐MLV reverse transcriptase as disclosed herein (“Mut D9 ).
[208] For non‐hot start (“NON‐HS‐RT”) reaction cond itions, reaction mixtures minus proteins (reverse transcriptase and RNaseOut) were inc ubated at 65°C for 5 minutes, followed by a 10 minute incubation on ice. RNaseOu t and reverse transcriptase enzyme were added to each reaction, and the reactions were then incubated at room temperature for 10 minutes. This was followed by an additional incubation at 50°C for 50 minutes, and then all reactions were heat killed at 95°C for 10 minutes.
[209] For manual hot start (“HS‐RT”) reaction conditio ns, reaction mixtures minus proteins (reverse transcriptase and RNaseOut) were incubated at 65°C for 5 minutes, followed by 10 minute incubation on ice. RNaseOut was added to ea ch reaction, and the reactions were incubated at 60°C for 10 minutes in the absence of reverse transcriptase. Reverse transcriptase enzymes were then added directly to the reactions while incubating at 60°C and the reactions were allowed to proceed at 60°C for 50 minutes. All reactions were then heat killed at 95°C for 10 minutes.
[210] Using the cDNA products from the above‐mentioned re verse transcription reactions, PCR mixtures were prepared. Briefly, 1 µL of the a bove RT reactions was added to 24 µL of a PCR mixture. PCR reactions were set up as recommen ded by the manufacturer using Platinum Taq DNA Polymerase High Fidelity (Life Techn ologies, Cat. No. 11304102) and amplified for 30 cycles. Gene‐specific primers for the pol E gene were used for PCR and resulted in a 1 kb fragment. Primer sequences we re as follows: Forward
(AGCGCCAGACATCGAGGGCGTATATGAGAC) and Reverse (TGGTGAGACTG GAGAATGGTGTTG). Gel products were visualized using 10 µL of each P CR reaction on a 2% E‐gel (Life
Technologies, Cat. No. G501802) As Figure 5 demonstrates, all three reverse transcrip tases produced transcripts using 10‐100 ng template DNA when incubated at room temperature a nd 50°C (see “NON‐HS‐RT” reactions), even in the absence of any primer (1), and produced similar amounts of 1 kb cDNA using either (2) oligo(dT) 20 primer; (3) locked nucleic acid (LNA) T20 pri mer, and (4) gene specific primer with 50‐100 ng template DNA. For the “HS‐RT” reactions, the 1 kb cDNA was not produced by SSIII for 10, 50, or 100 ng t emplate DNA in the absence of primer or with the addition of any of the primers (2, 3, or 4). The other commercially available RT (“M‐ RT”) also did not produce any cDNA in the absence of primer and only produced trace amounts of cDNA for 10, 50, or 100 ng template DNA when either the LNA T20 primer or the gene specific primers were used. Mutant M‐MLV Mut D9 (SEQ ID NO:4) on the other hand produced significant amounts of cDNA for 10 ng templ ate DNA when either the LNA T20 primer or the gene specific primers were used and a lso produced significant amounts of cDNA for 50 and 100 ng of template DNA for all th ree of the primers (2, 3, and 4) that were tested. This shows that Mut D9 not only functions at 60°C, but is also able to reverse transcribe template DNA using non‐specific (e.g., dT or LNA) primers as well as specific
primers types. Mut D9’s ability to produce more products with only 10 ng input RNA than either wild type M‐MLV reverse transcriptase or any of the other commercially available (“conventional”) mutant M‐MLV RTs further indicat es an increase in sensitivity. [211] Moreover, the ability to carry out reverse transcript ion reactions at higher
temperatures, such as at 60°C, helps to prevent pri merless cDNA synthesis which was visible for all RTs tested in the “NON‐HS‐RT” reactio ns. Thus, having an RT that is able to perform efficiently at 60°C, such as those disclosed herein, provides the benefit of reducing the amount of non‐specific priming due to self‐priming events that can often occur during RT reactions. This reduction in primerless cDNA is gre atly enhanced at elevated temperatures (e.g., at 50°C, 55°C, 60°C, etc.).
Example 5
Mutant Reverse Transcriptase Performance in the Presen ce of Inhibitors
[212] A similar assay as that described in Example 2 was performed in the presence of various inhibitors. RT reaction temperature was 37 ° C for wild type M‐MLV, while the reaction temperature for other commercially available mutant M‐MLV RTs (“SSIII” and “C‐ RT”), and Mut D9 was 50°C. Each RT reaction wa s carried out for 60 minutes. The RT inhibitors tested include SDS (0.006‐0.01%), ethanol (26‐30%), humic acid (21‐25 ng/µL), bile salts (0.16‐0.2%), heparin (0.0031‐0.0042 U/µL), a nd hematin (46‐50 µM). As Figure 6 demonstrates, wild type M‐MLV is not functional at all concentration of SDS, humic acid, bile salts, and hematin. It is slightly function in ethan ol but cannot synthesize a full length 0.5 kb cDNA. However, in the presence of heparin, wild type M‐MLV is able to synthesize the 0.5 kb cDNA. SSIII is not functional at all concentration o f SDS, humic acid, and hematin. It is slightly functional in ethanol and bile salts but cannot synt hesize a full length 0.5 kb cDNA. It can reverse transcribe up to 1.5 kb when heparin is pre sent. Mut D9 shows greater activity than both wild type M‐MLV and SSIII at all concentratio ns of inhibitors tested. Mut D9 compared to other commercially available RTs (i.e., C‐RT) di splays greater activity at all concentrations of inhibitors tested with the exception of ethanol a nd heparin where activity is
approximately equal.
[213] The % activity of the RTs tested in the presence o f the various inhibitors as described above was quantitated by densitometry using TotalLab TL100 software. Volume intensity of
each band was summed in each lane. The volume in tensity of no inhibitor lanes was set to 100% and lanes with inhibitors were normalized as % of no inhibitors to give % activity. Figure 7 shows the comparison of RT activities of t he different RTs shown in Figure 6.