Effect of the SinR protein on the expression of the Bacillus subtilis 168 lytABC operon

Transcription of the lytABC operon was determined by extension of primers on RNAs isolated from strains bearing a deficient sinR gene. A SinR null mutant, in which part of the sinR gene was deleted, exhibits a pattern identical to that characteristic of FlaB (SigD) deficient mutants, i.e., loss of the signal corresponding to the SigD-dependent promoter, but not of that recognized by the SigA form of the RNA polymerase. However, strains bearing either flaD1 or flaD2, two different point mutations of gene sinR, were characterized by a complete loss of signals corresponding to both promoters. Thus, modified FlaD1 and FlaD2 proteins behave like a repressor affecting the expression of lytABC more severely than does the absence of SinR, The most obvious interpretation of this observation is a direct interaction between the SinR protein and the promoters recognized by the SigD form of the RNA polymerase.