The complete cps gene cluster from Streptococcus thermophilus NCFB 2393 involved in the biosynthesis of a new exopolysaccharide

The cpsFGHIJKL genes from the cps cluster of Streptococcus thermophilus NCF B 2393 involved in the biosynthesis of EPS were identified, cloned and nucl eotide sequenced. The complete cps cluster is contained on an similar to 11 .2 kb chromosomal region which contains 12 ORFs, including the previously c loned cpsABCDE genes. Functions were assigned to some of the predicted gene products on the basis of homology to known sequences as follows: cpsK enco des a protein thought to be involved in the polymerization and export of th e polysaccharide; cpsE, cprF, cpsG, cpsH, cpsl and cpsJ encode putative sug ar transferases. Two insertion sequences, IS1193 and ISS1, were identified within and flanking the 3' end of the cps cluster respectively. Analysis of the expression of the cpsE gene in Escherichia coil demonstrated that it e ncodes a glucose-1-phosphate transferase; the enzyme which catalyses the fi rst step in EPS biosynthesis in S. thermophilus NCFB 2393.