To obtain a new polynucleotide which possesses high homology to the nucleic acid that codes for fol C polypeptide containing a specific amino acid sequence and is useful for protection or the like against infection caused by bacteria, e.g. Streptococcus pneumoniae or the like.

This new polynucleotide is a polynucleotide newly isolated from fol C which is composed of the polynucleotide having at least 70% of homology to the polynucleotide that codes for the polypeptide containing the amino acid sequence of the formula or the polynucleotide having at least 70% of homology to the polynucleotide that codes for the maturation polypeptide similar to that expressed by the fol C gene contained in the deposit strain of Streptococcus pneumoniae and is useful for protection or the like against infection caused by bacteria, e.g. Streptococcus pneumoniae or the like. This polynucleotide is obtained by probing the chromosome DNA library originated from Streptococcus pneumoniae with the labelled oligonucleotide arising from the partial sequence.