Characterization of glucosyltransferase expressed from a Streptococcus sobrinus gene cloned in Escherichia coli

The gene encoding a glucosyltransferase which synthesized water-insoluble glucan, gtfI, previously cloned from Streptococcus sobrinus strain MFe28 (mutans serotype h) into a bacteriophage λ vector, was subcloned into the plasmid pBR322. The recombinant plasmid was stable in Escherichia coli and gtfI was efficiently expressed. The GTF-I expressed in E. coli was compared to the corresponding enzymes in S. sobrinus strains MFe28 (serotype h), B13 (serotype d) and 6715 (serotype g) and shown to resemble them closely in molecular mass and isoelectric point. The insoluble glucan produced by GTF-I from recombinant E. coli consisted of 1,3-α-D-glycosyl residues (~90%). An internal fragment of the gtfI gene was used as a probe in hybridization experiments to demonstrate the presence of homologous sequences in chromosomal DNA of other streptococci of the mutans group.