Functional analysis of the Bacillus subtilis y shD gene, a mutS paralogue

In the course of the Bacillus subtilis genome sequencing project, an ORF called yshD was identified, and its product was classified as a mismatch repair protein. Further analysis of the YshD primary sequence showed that the protein belongs to the MutS2 protein family, sharing a high degree of identity with the Thermootoga Inaritima protein TM1278 (34%) and with the so-called MutS2 protein sl11772 of Synechocystis (32%). The COG1193 family of MutS-like proteins is made up of polypeptides that have been predicted from genomic sequencing data from various prokaryotes, but their biological role has not yet been analysed. The functional study of yshD revealed that the gene is constitutively transcribed during the life cycle of B. subtilis, and in minimal medium expression remains at appreciable levels until very late in stationary phase. Fluctuation tests with yshD knock-out mutants did not indicate any role for the protein in preventing the accumulation of spontaneous forward mutations to RifR, nor was any functional interaction with MutS or MutL suggested in fluctuation experiments with mutants lacking combinations of the three genes. Nevertheless, the mutation spectrum observed in the rpoB gene in the deltayshD strain has some characteristic features. The gene does not seem to be involved in the prevention of interspecific recombination in transformation-competent cells.