ALTERNATE PROMOTERS DIRECT STRESS-INDUCED TRANSCRIPTION OF THE BACILLUS-SUBTILIS CLPC OPERON

clpC of Bacillus subtilis is part of an operon containing six genes, N orthern blot analysis suggested that all genes are co-transcribed and encode stress-inducible proteins. Two promoters (P-A and P-B) were map ped 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 expresse d in a sigma(B)-dependent manner. This is the first evidence that sigm a(B) in B. subtilis is involved in controlling the expression of a gen e whose counterpart, clpB, is subject to regulation by sigma(32) in Es cherichia coli, indicating a new function of sigma(B)-dependent genera l stress proteins, P-B deviated from the consensus sequence of sigma(B ) promoters and was only slightly induced by starvation conditions. Ne vertheless, strong induction by heat, ethanol, and salt stress occurre d at the sigma(B)-dependent promoter, whereas the vegetative promoter was only weakly induced under these conditions. However, in a sigB mut ant, the sigma(A)-like promoter became inducible by heat and ethanol s tress, completely compensating for sigB deficiency. Only the downstrea m sigma(A)-like promoter was induced by certain stress conditions such as hydrogen peroxide or puromycin. These results suggest that novel s tress-induction mechanisms are acting at a vegetative promoter. Involv ement of additional elements in this mode of induction are discussed.