STREPTOCOCCUS-SALIVARIUS ATCC-25975 POSSESSES AT LEAST 2 GENES-CODINGFOR PRIMER-INDEPENDENT GLUCOSYLTRANSFERASES

Fractionation of the culture medium showed that Streptococcus salivari us ATCC 25975 secreted a glucosyl-transferase (Gtf) that was primer in dependent, On the basis of this observation, a gene library of S. sali varius chromosomal DNA cloned into lambda L47.1 was screened for a gen e(s) coding for such an activity. As a result of this screening proces s, two new gtf genes, gtfL and gtfM, both of which coded for primer-in dependent Gtf activities, were isolated, GtfL produced an insoluble gl ucan that was refractory to digestion by the endo-(1 --> 6)-alpha-D-gl ucanase of Chaetonium gracile, while GtfM produced a soluble glucan th at was readily degraded by the glucanase. Comparison of the deduced am ino acid sequences of gtfL and gtfM with 10 other available Gtf sequen ces allowed the relatedness of the conserved catalytic regions to be a ssessed, This analysis showed that the 12 enzymes did not form cluster s based on their primer dependencies dr on their product solubilities, Further analysis of the YG repeats in the C-terminal glucan-binding d omains of GtfJ, GtfK, GtfL, and GtfM from S. salivarius showed that th ere was strong homology between a block of contiguous triplet YG repea ts present in the four alleles. These blocks of YG repeats were coded for by a region of each gene that appeared to have arisen as a result of a recent duplication event(s).