Genetic linkage among cloned genes of Streptococcus mutans.

Mapping vectors containing antibiotic resistance markers inserted adjacent to or within different cloned genes from Streptococcus mutans were used to determine the relative positions of these genes on the chromosome. The gtfA, ftf, and scrB genes were inserted into streptococcal mapping vector pVA891 adjacent to an Emr gene, whereas the Emr marker was inserted directly into the gtfB gene. These chimeric plasmids were transformed into S. mutans GS-5, selecting for Emr transformants. To determine the positions of the cloned genes relative to each other, it was necessary to construct plasmids labeled with a different antibiotic resistance marker. Thus, a Tetr gene was inserted adjacent to gtfB in the appropriate mapping vector and within the ftf and scrB genes with a mini-Mu transposon (Mu dT). The chimeric plasmids were transformed into the appropriate Emr recipients, and the DNA from the resulting Emr Tetr transformants was used in linkage studies. Based on the cotransfer data, gtfB was not closely linked to gtfA, ftf, or scrB. However, gtfA cotransferred with ftf and scrB at frequencies of approximately 96 and 80%, respectively. The percent cotransfer of ftf and scrB was approximately 92. These data indicate that the three genes are clustered on the GS-5 chromosome, with ftf located between gtfA and scrB. Little, if any, linkage was observed between these genes and a variety of other random markers.