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Summary: 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 (PA and PB) were mapped upstream of the first gene. PA resembles promoters recognized by the vegetative RNA polymerase E[sigma]A. The other promoter (PB) was shown to be dependent on [sigma]B, the general stress [sigma] factor in B. subtillis, 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. PB 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.

(C) 1996 Blackwell Science Ltd.