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.