The htpG gene of Bacillus subtilis belongs to class III heat shock genes and is under negative control.

We show that the htpG gene of Bacillus subtilis is induced by heat, as has been reported for the Escherichia coli homolog. Analysis of different mutants revealed that the htpG gene belongs to class III heat shock genes in B. subtilis. An about 10-fold induction after thermal upshock was found at the levels of both transcription and translation, and this induction resulted from enhanced synthesis of mRNA. By primer extension, we identified one potential transcription start site immediately downstream of a putative sigmaA-dependent promoter which became activated after thermal upshift. Northern blot analysis revealed that htpG is part of a monocistronic transcriptional unit. An operon fusion where the complete region between htpG and its upstream gene was fused to the bgaB reporter gene accurately reflected htpG expression. Analysis of this fusion revealed that, in contrast to other class III heat shock genes, htpG was not induced by osmotic upshock, by ethanol, or by oxygen limitation, suggesting that it belongs to a subgroup within class III. Deletion of the region upstream of the putative promoter resulted in an enhanced basal level of htpG expression, but the 10-fold induction was retained, suggesting that the upstream sequences are involved in the regulation of expression in the absence of heat shock.