Molecular basis of thermosensing: a two-component signal transduction thermometer in Bacillus subtilis

Both prokaryotes and eukaryotes respond to a decrease in temperature with the expression of a specific subset of proteins. Although a large body of information concerning cold shock‐induced genes has been gathered, studies on temperature regulation have not clearly identified the key regulatory factor(s) responsible for thermosensing and signal transduction at low temperatures. Here we identified a two‐component signal transduction system composed of a sensor kinase, DesK, and a response regulator, DesR, responsible for cold induction of the des gene coding for the Δ5‐lipid desaturase from Bacillus subtilis . We found that DesR binds to a DNA sequence extending from position −28 to −77 relative to the start site of the temperature‐regulated des gene. We show further that unsaturated fatty acids (UFAs), the products of the Δ5‐desaturase, act as negative signalling molecules of des transcription. Thus, a regulatory loop composed of the DesK–DesR two‐component signal transduction system and UFAs provides a novel mechanism for the control of gene expression at low temperatures.