THE CPSABCDE GENES INVOLVED IN POLYSACCHARIDE PRODUCTION IN STREPTOCOCCUS-SALIVARIUS SSP THERMOPHILUS STRAIN NCBF-2393

A 4074-bp EcoRI fragment of Streptococcus salivarius sap. thermophilus (S. thermophilus) chromosomal DNA containing genes involved in exocel lular polysaccharide (EPS) was identified and cloned. The nucleotide s equence of this fragment was determined and found to contain one parti al and four complete open reading frames. These were designated cpsA, cpsB, cpsC, cpsD and cpsE and encoded proteins of > 130, 243, 230, 246 and 455 amino acids, respectively, that showed homology with the gene s of the cps cluster, involved in polysaccharide biosynthesis, in Stre ptococcus pneumoniae Type 19F. The cpsA gene is predicted to encode a transcriptional regulator, while cpsC and cpsD are predicted to encode proteins involved in polysaccharide polymerization and export. The cp sE gene is likely to encode the phosphate-prenyl glycosyl-1-phosphate transferase catalyzing the first step in polysaccharide biosynthesis i n S. thermophilus. Southern blot analysis revealed that cpsE is found only In polysaccharide producing strains of S. thermophilus.