The σE‐mediated response to extracytoplasmic stress in Escherichia coli is transduced by RseA and RseB, two negative regulators of σE

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Abstract
The extracytoplasmic stress response in Escherichia coli is controlled by the alternative sigma factor, σE. σE activity is uniquely induced by the accumulation of outer membrane protein precursors in the periplasmic space, and leads to the increased production of several proteins, including the periplasmic protease DegP, that are thought to be required for maintaining cellular integrity under stress conditions. Genetic and biochemical experiments show that σE activity is under the control of three genes, rseABC (for regulator of sigma E), encoded immediately downstream of the sigma factor. Deletion of rseA leads to a 25‐fold induction of σE activity. RseA is predicted to be an inner membrane protein, and the purified cytoplasmic domain binds to and inhibits σE‐directed transcription in vitroindicating that RseA acts as an anti‐sigma factor. Deletion of rseB leads to a slight induction of σE, indicating that RseB is also a negative regulator of σE. RseB is a periplasmic protein and was found to co‐purify with the periplasmic domain of RseA, indicating that RseB probably exerts negative activity on σE through RseA. Deletion of rseC, in contrast, has no effect on σE activity under steady‐state conditions. Under induction conditions, strains lacking RseB and/or C show wild‐type induction of σE activity, indicating either the presence of multiple pathways regulating σE activity, or the ability of RseA alone to both sense and transmit information to σE.

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