Transcriptional Regulation of Bacillus subtilis Glucose Starvation-Inducible Genes: Control of gsiA by the ComP-ComA Signal Transduction System

The Bacillus subtilis glucose starvation-inducible transcription units, gsi4 and gsiB, were characterized by DNA sequencing, transcriptional mapping, mutational analysis, and expression in response to changes in environmental conditions. The gsiA operon was shown to consist of two genes, gsiAA and gsiAB, predicted to encode 44.9- and 4.8-kDa polypeptides, respectively. The gsiB locus contains a single cistron which encodes a prbtein of unusual structure; most of its amino acids are arranged in five highly conserved, tandemly repeated units of 20 amino acids. The 5 ' ends ofgsiA and gsiB mRNAs were located by primer extension analysis; their locations suggest that both are transcribed by RNA polymerase containing sigma A. Expression of both gsiA and gsiB was induced by starvation for glucose or phosphate or by addition of decoyinine, but only gsi4 was induced by exhaustion of nutrient broth or by amino acid starvation. Regulation ofgsi4 expression was shown to be dependent upon the two-component signal transduction system ComP-ComA, which also controls expression of genetic competence genes. Mutations in mecA bypassed the dependency of gsi4 expression on ComA. Disruption of gsiA relieved glucose repression of sporulation but did not otherwise interfere with sporulation, development of competence, motility, or glucose starvation survival. We propose that gsiA4 and gsiB are members of an adaptive pathway of genes whose products are involved in responses to nutrient deprivation other than sporulation