Two genes from Bacillus subtilis under the sale control of the general stress transcription factor σB

The general stress response of Bacillus subtilis is triggered by a variety of environmental and metabolic stresses which activate the sigma(B) transcription factor. Among the more than 100 genes controlled by sigma(B) (the csb genes), the functions identified thus far include resistance to oxidative stress, resistance to protein denaturation and resistance to osmotic stress. To understand the breadth of functions in which csb genes participate, the transcriptional organization and predicted products of two such genes previously identified in a screen for sigma(B)-dependent lacZ fusions were analysed. The csb-22::Tn917lacZ and csb-34::Tn917lacZ fusions are unusual among csb genes in that their expression appears to be completely dependent upon sigma(B). By plasmid-integration experiments, fusion analyses and site-directed mutagenesis, stress-inducible, sigma(B)-dependent promoters for both these fusions were identified. The csb-34 fusion marked an ORF (yxcC or csbC) which by sequence analysis lay in a monocistronic transcriptional unit. This ORF encoded a predicted 461-residue product which had high identity with Class I sugar transporters of the major facilitator superfamily. It was speculated that the csbC product could serve either a nutritional or an osmotic protection function. In contrast, the csb-22 fusion identified an ORF (ywmG or csbD) which appeared to be the second gene of a two-gene operon. This ORF encoded a predicted 62-residue product which resembled a small Escherichia coli protein of unknown function. The sigma(B)-dependent promoter lay immediately upstream from csbD and appeared to be an internal promoter for the operon.