Isolation and characterization of the Streptococcus mutans gtfC gene, coding for synthesis of both soluble and insoluble glucans.

The intact gtfC gene from Streptococcus mutans GS-5 was isolated in Escherichia coli in plasmid vector pUC18. The glucosyltransferase activity expressed by the gene synthesized both low-molecular-weight water-soluble glucan and insoluble glucan in a primer-independent manner. Purification of the enzyme by procedures that minimize proteolytic digestion yielded a purified preparation with a molecular weight of 140,000. Insertional inactivation of the gtfC gene with a streptococcal erythromycin resistance gene fragment followed by transformation of strain GS-5 suggested that the gtfC gene product was required for sucrose-dependent colonization in vitro. In addition, evidence for the presence of a third gtf gene coding for soluble glucan synthesis was obtained following the construction of mutants containing deletions of both the gtfB and gtfC genes.