CcpB, a novel transcription factor implicated in catabolite repression in Bacillus subtilis

Recent work has shown that in Bacillus subtilis catabolite repression of several operons is mediated by a mechanism dependent on DNA-binding protein CcpA complexed to a seryl-phosphorylated derivative of HPr [HPr(Ser-P)], the small phosphocarrier protein of the phosphoenolpyruvate-sugar phosphotransferase system. In this study, it was found that a transposon insertional mutation resulted in the partial loss of gluconate (gnt) and xylose (xyl) operon catabolite repression by glucose, mannitol, and sucrose. The transposon insertion was localized to a gene, designated ccpB, encoding a protein 30% identical to CcpA, and relief from catabolite repression was shown to be due to the absence of CcpB rather than to the absence of a protein encoded by a downstream gene within the same operon. The relative intensities of CcpA- and CcpB-mediated catabolite repression depended on growth conditions. On solid media, and when cells were grown in liquid media with little agitation, CcpB and CcpA both proved to function in catabolite repression. However, when cells were grown in liquid media with much agitation, CcpA alone mediated catabolite repression. Like CcpA, CcpB appears to exert its catabolite-repressing effect by a mechanism dependent on the presence of HPr(Ser-P).