DNA homology of surface protein antigen A gene in mutans streptococci

1. A recombinant plasmid, pYA724, containing an 8.45 kb DNA fragment encoding surface protein antigen A (spaA) from Streptococcus sobrinus 6715 was used to examine the DNA homology of the spaA gene with chromosomal DNA of various mutans streptococci strains. 2. Restriction endonuclease BamHI-digested pYA724 DNA was radio-labeled by nick-translation, and a DNA-DNA hybridization experiment was carried out. pYA724 DNA hybridized with chromosomal DNA of serotypes a, c, d, e, f and g strains, but not with b by dot DNA-hybridization and Southern blot DNA hybridization. 3. Chromosomal DNAs were isolated from several serotype c Streptococcus mutans strains, digested with BamHI, and analyzed by Southern blot DNA hybridization. pYA724 DNA hybridized with different sizes and numbers of BamHI-digested DNA fragments of the chromosomal DNAs. 4. These data indicated that all mutans streptococci strains except serotype b have DNA homologous with the spaA gene, although within the same serotype strain the spaA gene has a diversity of arrangement within the chromosome.