The complete nucleotide sequence (3, 747bp) of the dextranase gene (
dexA) and flanking regions of the chromosome of
Streptococcus mutans Ingbritt (serotype c) were determined. The open reading frame for
dexA was 2, 550bp, ending with a stop codon TGA. A putative ribosome-binding site, promoter preceding the start codon, and potential stem-loop structure were identified. The presumed dextranase protein (DexA) consisting of 850 amino acids was estimated to have a molecular size of 94, 536 Da and a pI of 4.79. The nucleotide sequence and the deduced amino acid sequences of
S. mutans dexA exhibited homologies of 57.8% and 47.0%, respectively, to those of
Streptococcus sobrinus dex. The homologous region of
dex of
S. sobrinus was in the N-terminal half. The C terminus of DexA consisted of a hexapeptide LPQTGD, followed by 7 charged amino acids, 21 amino acids with a strongly hydrophobic character, and a charged hexapeptide tail, which have been reported as a common structure of C termini of not only the surface-associated proteins of Gram-positive cocci but also the extracellular enzymes such as β-fructosidase of
S. mutans and dextranase of
S. sobrinus. The DexA protein had no significant homology with the glucosyltransferases, the glucan-binding protein, or the dextranase inhibitor of mutans streptococci.
抄録全体を表示