SPECIFIC RECOGNITION OF THE BACILLUS-SUBTILIS GNT CIS-ACTING CATABOLITE-RESPONSIVE ELEMENT BY A PROTEIN COMPLEX FORMED BETWEEN CCPA AND SERYL-PHOSPHORYLATED HPR

Catabolite repression of various Bacillus subtilis catabolic operons w hich carry a cis-acting catabolite-responsive element (CRE), such as t he gnt operon, is mediated by CcpA, a protein belonging to the GalR-La cl family of bacterial transcriptional repressors/activators, and the seryl-phosphorylated form of HPr, a phosphocarrier protein of the phos phoenolpyruvate:sugar phosphotransferase system. Footprinting experime nts revealed that the purified CcpA protein interacted with P-ser-HPr to cause specific protection of the gnt CRE against DNase I digestion. The specific recognition of the gnf CRE was confirmed by the results of footprinting experiments using mutant gnt CREs carrying one of the following base substitutions within the CRE consensus sequence: G to T at position +149 or C to T at position +154 (+1 is the gnt transcript ion initiation nucleotide). The two mutant CREs causing a partial reli ef from catabolite repression were not protected by the CcpA/P-ser-HPr complex in footprinting experiments. Based on these and previous find ings, we propose a molecular mechanism underlying catabolite repressio n in B. subtilis mediated by CcpA and P-ser-HPr.