Molecular cloning and characterization of the glucosyltransferase C gene (gtfC) from Streptococcus mutans LM7

A glucosyltransferase (GTF) gene, designated gtfC, was cloned from Streptococcus mutans LM7. Its gene product was detected by screening a bacteriophage lambda library with rabbit antiserum raised against S. mutans LM7 extracellular proteins. DNA isolated from the immunopositive recombinant phage revealed two S. mutans chromosomal EcoRI fragment inserts, 8.1 and 4.7 kilobase pairs in size. Escherichia coli minicell analyses revealed the approximate position and direction of transcription of the gtfC gene. The gene product was determined to be a polypeptide of about 150 kilodaltons which synthesized a water-soluble glucan. Restriction endonuclease mapping and DNA hybridization indicated a repeated region of DNA corresponding to a portion of the coding region of gtfC immediately downstream from the intact gtfC locus on the chromosome. A 300-base-pair gtfC-specific probe showed that the gene and the putative duplicated sequence were present in S. mutans serotypes c, e, and f, but not in other related oral streptococci which had GTF activity. In addition, the gtfC determinant displayed homology to sequences corresponding to the carboxy-terminal coding region of a gene (gtfB) encoding a GTF activity that synthesized water-insoluble glucans. These data suggest that at least one class of GTF genes may be present in multiple copies in S. mutans and, further, that GTF genes may contain conserved sequences internal to their coding regions.