Summary: 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 ( and ) from ATCC 25975 as well as the sequence of , which encodes a primer-dependent GTF that synthesizes an insoluble product (a GTF-I). In this communication we report the sequence of which encodes 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 those of seven other streptococcal Gtfs and an unrooted phylogenetic tree constructed. This analysis suggested that Gtfs with similar product specificities do not form phylogenetic clusters and was consistent with currently accepted phylogenetic schemes. The tree was tested by constructing a series of “sub-trees” from different blocks of the alignment. Evidence was obtained for recombination events involving and from GS-5, and from as well as the genes from and The recombination events between and and between the two genes, were confirmed by examining divergences at silent sites.


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