degS (hhoB) is an essential Escherichia coli gene whose indispensable function is to provide sigma(E) activity

DegS (HhoB), a putative serine protease related to DegP/HtrA, regulates the basal and induced activity of the essential Escherichia coli sigma factor sigma (E), which is involved in the cellular response to extracytoplasmic s tress. DegS promotes the destabilization of the sigma (E)-specific anti-sig ma factor RseA, thereby releasing sigma (E) to direct gene expression. We d emonstrate that degS is an essential E. coli gene and show that the essenti al function of DegS is to provide the cell with sigma (E) activity. We also show that the putative active site of DegS is periplasmic and that DegS re quires its N-terminal transmembrane domain for its sigma (E)-related functi on.