The Bacillus subtilis heat shock stimulon

All organisms respond to a sudden increase in temperature by the so-called heat shock response. This response results in the induction of a subset of genes, designated heat shock genes coding for heat shock proteins, which allow the cell to cope with the stress regimen. Research carried out during the last 10 years with eubacteria has revealed that the heat shock genes of a given species fall into different classes (regulons), where each class is regulated by a different transcriptional regulator, which could be an alternative sigma factor, a transcriptional activator, or a transcriptional repressor. All regulons of a single species constitute the heat shock stimulon. In Bacillus subtilis, more than 200 genes representing over 7% of the transcriptionally active genes are induced at least 3-fold in response to a heat shock. This response becomes apparent within the first minute after exposure to heat stress, is transient, and is coordinated by at least 5 transcriptional regulator proteins, including 2 repressors, an alternate sigma-factor, and a 2-component signal transduction system. A detailed analysis of the regulation of all known heat shock genes has shown that they belong to at least 6 regulons that together comprise the B. subtilis heat shock stimulon. Potential thermosensors are discussed in this article.