Characterization of glucose-repression-resistant mutants of Bacillus subtilis: identification of the glcR gene

In Bacillus subtilis, carbon catabolite repression (CCR) is mediated by the pleiotropic repressor CcpA and by ATP-dependent phosphorylation of the HPr protein of the phosphotransferase system (PTS). In this study, we attempte d to identify novel genes that are involved in the signal transduction path way that ultimately results in CCR in the presence of repressing carbon sou rces such as glucose. Seven mutants resistant to glucose repression of the levanase operon were isolated and characterized. All mutations were trans-a cting and pleiotropic as determined by analyzing CCR of beta -xylosidase an d of the sacPA and bglPH operon. Moreover, all mutations specifically affec ted repression exerted by glucose but not by other sugars. The mutations we re mapped to three different loci on the genetic map, ptsG, glcR, and pgi. These three genes encode proteins involved in glucose metabolism. A novel r epressor gene, glcR (ywpI), defined by two mutations, was studied in more d etail. The glcR mutants exhibit loss of glucose repression of catabolic ope rons, a deficiency in glucose transport, and absence of expression of the p tsG gene. The mutant GlcR proteins act as super-repressors of ptsG expressi on.