Regulation of the Bacillus subtilis heat shock gene htpG is under positive control

The heat shock genes of Bacillus subtilis are assigned to four classes on the basis of their regulation mechanisms. While classes I and III are negatively controlled by two different transcriptional repressors, class II is regulated by the alternative sigma factor sigma(B). All heat shock genes with unidentified regulatory mechanisms, among them htpG, constitute class IV. Here, we show that expression of htpG is under positive control. We identified a DNA sequence (GAAAAGG) located downstream of the sigma(A)-dependent promoter of htpG. The heat inducibility of the promoter could be destroyed by inversion, nucleotide replacements, or removal of this DNA sequence. Fusion of this sequence to the vegetative lepA promoter conferred heat inducibility. Furthermore, we were able to show that the heat induction factor is dependent on the absolute temperature rather than the temperature increment and that nonnative proteins within the cytoplasm fail to induce htpG.