Molecular characterization of a cluster of at least two glucosyltransferase genes in Streptococcus salivarius ATCC 25975

The oral micro-organism Streprococcus salivarius ATCC 25975 synthesizes extracellular glucosyltransferases (GTFs) which polymerize the glucose moiety of sucrose into glucan polymers. Two separate genes encoding the activities of a GTF-I (a GTF that synthesizes an insoluble product) and a GTF-S (a GTF that synthesizes soluble product) were cloned into bacteriophage λL47.1. The inserts in the λ-clones were characterized by restriction mapping and Southern hybridization and were found to overlap, implying that the two genes lay very close to one another on the S. salivarius chromosome. Both genes were subcloned into phagemid vector pIBI30 where they were expressed at a high level. The GTF-I-encoding gene was named gtfJ and the GTF-S-encoding gene, gtfK. Nucleotide sequencing showed that gtfJ and most probably gtfK were closely related to the gtS genes of the mutans streptococci. Sequence alignment also indicated that gtfK lay very close to and downstream from gtfJ, and that both were transcribed in the same direction.