THE SIGMA(E)-MEDIATED RESPONSE TO EXTRACYTOPLASMIC STRESS IN ESCHERICHIA-COLI IS TRANSDUCED BY RSEA AND RSEB, 2 NEGATIVE REGULATORS OF SIGMA(E)

The extracytoplasmic stress response in Escherichia coli is controlled by the alternative sigma factor, sigma(E) sigma(E) activity is unique ly induced by the accumulation of outer membrane protein precursors in the periplasmic space, and leads to the increased production of sever al proteins, including the periplasmic protease DegP, that are thought to be required for maintaining cellular integrity under stress condit ions. Genetic and biochemical experiments show that sigma(E) activity is under the control of three genes, rseABC (for (r) under bar egulato r of (s) under bar igma (E) under bar), encoded immediately downstream of the sigma factor. Deletion of rseA leads to a 25-fold induction of sigma(E) activity. RseA is predicted to be an inner membrane protein, and the purified cytoplasmic domain binds to and inhibits sigma(E)-di rected transcription in vitro, indicating that RseA acts as an anti-si gma factor. Deletion of rseB leads to a slight induction of sigma(E), indicating that RseB is also a negative regulator of sigma(E). RseB is a periplasmic protein and was found to co-purify with the periplasmic : domain of RseA, indicating that RseB probably exerts negative activi ty on sigma(E) through RseA. Deletion of rseC, in contrast, has no eff ect on sigma(E) activity under steady-state conditions. Under inductio n conditions, strains lacking RseB and/or C show wild-type induction o f sigma(E) activity, indicating either the presence of multiple pathwa ys regulating sigma(E) activity, or the ability of RseA alone to both sense and transmit information to sigma(E).