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

Both prokaryotes and eukaryotes respond to a decrease in temperature with t he expression of a specific subset of proteins. Although a large body of in formation concerning cold shock-induced genes has been gathered, studies on temperature regulation have not clearly identified the key regulatory fact or(s) responsible for thermosensing and signal transduction at low temperat ures. Here we identified a two-component signal transduction system compose d of a sensor kinase, DesK, and a response regulator, DesR, responsible for cold induction of the des gene coding for the Delta5-lipid desaturase from Bacillus subtilis, We found that DesR binds to a DNA sequence extending fr om position -28 to -77 relative to the start site of the temperature-regula ted des gene. We show further that unsaturated fatty acids (UFAs), the prod ucts of the Delta5-desaturase, act as negative signalling molecules of des transcription. Thus, a regulatory loop composed of the DesK-DesR two-compon ent signal transduction system and UFAs provides a novel mechanism for the control of gene expression at low temperatures.