Alternate promoters direct stress-induced transcription of the Bacillus subtilis clpC operon
1996
Kruger, E. | Msadek, T. | Hecker, M.
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 sigmaA. The other promoter (P(B)) was shown to be dependent on sigmaB, the general stress a factor in B. subtilis, suggesting that clpC, a potential chaperone, is expressed in a sigmaB-dependent manner. This is the first evidence that sigmaB in B. subtilis is involved in controlling the expression of a gene whose counterpart, clpB, is subject to regulation by sigma32 in Escherichia coli, indicating a new function of sigmaB-dependent general stress proteins. P(B) deviated from the consensus sequence of sigmaB promoters and was only slightly induced by starvation conditions. Nevertheless, strong induction by heat, ethanol, and salt stress occurred at the sigmaB-dependent promoter, whereas the vegetative promoter was only weakly induced under these conditions. However, in a sigB mutant, the sigmaA-like promoter became inducible by heat and ethanol stress, completely compensating for sigB deficiency. Only the downstream sigmaA-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.
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