SEQUENCE OF THE GTFK GENE OF STREPTOCOCCUS-SALIVARIUS ATCC-25975 AND EVOLUTION OF THE GTF GENES OF ORAL STREPTOCOCCI

Many strains of oral streptococci secrete glucosyltransferases (GTFs) that polymerize sucrose into glucans that form an integral part of the plaque matrix on the tooth surface. Recently, we reported the cloning of two closely linked GTF-encoding genes (gtfJ and gtfK) from Strepto coccus salivarius ATCC 25975 as well as the sequence of gtfJ, which en codes a primer-dependent GTF that synthesizes an insoluble product (a GTF-I). In this communication we report the sequence of gtfK, which en codes a primer-dependent GTF that synthesizes a soluble product (a GTF -S), as well as the sequence of a small downstream open reading frame of unknown function. The deduced sequence of GtfK was compared with th ose of seven other streptococcal Gtfs and an unrooted phylogenetic tre e constructed. This analysis suggested that Gtfs with similar product specificities do not form phylogenetic clusters and was consistent wit h currently accepted phylogenetic schemes. The tree was tested by cons tructing a series of 'sub-trees' from different blocks of the alignmen t. Evidence was obtained for recombination events involving gtfB and g tfC from S. mutans GS-5, gtfJ and gtfK from S. salivarius, as well as the gtFI genes from S. downei and S. sobrinus. The recombination event s between gtfB and gtfC, and between the two gtfI genes, were confirme d by examining divergences at silent sites.