Alternate promoters direct stress-induced transcription of the Bacillus subtilis clpC operon

clpC of Bacillus subtilis is part of an operon containing six genes, Northern blot analysis suggested that all genes are co-transcribed and encode stress-inducible proteins. Two promoters (P-A and P-B) were mapped upstream of the first gene, P-A resembles promoters recognized by the vegetative RNA polymerase E sigma(A). The other promoter (P-B) was shown to be dependent on sigma(B), the general stress sigma factor in B. subtilis, suggesting that clpC, a potential chaperone, is expressed in a sigma(B)-dependent manner. This is the first evidence that sigma(B) in B. subtilis is involved in controlling the expression of a gene whose counterpart, clpB, is subject to regulation by sigma(32) in Escherichia coli, indicating a new function of sigma(B)-dependent general stress proteins, P-B deviated from the consensus sequence of sigma(B) promoters and was only slightly induced by starvation conditions. Nevertheless, strong induction by heat, ethanol, and salt stress occurred at the sigma(B)-dependent promoter, whereas the vegetative promoter was only weakly induced under these conditions. However, in a sigB mutant, the sigma(A)-like promoter became inducible by heat and ethanol stress, completely compensating for sigB deficiency. Only the downstream sigma(A)-like promoter was induced by certain stress conditions such as hydrogen peroxide or puromycin. These results suggest that novel stress-induction mechanisms are acting at a vegetative promoter. Involvement of additional elements in this mode of induction are discussed.