Control of the alternative sigma factor σ^E in Escherichia coli

Signal transduction pathways that communicate information from the cell envelope to the cytoplasm of bacteria are crucial to maintain cell envelope homeostasis. In Escherichia coli, one of the key pathways that ensures the integrity of the cell envelope during stress and normal growth is controlled by the alternative sigma factor σ^E. Recent studies have elucidated the signal transduction pathway that activates σ^E in response to misfolded outer membrane porins. Unfolded porins trigger the degradation of the σ^E-specific antisigma factor RseA by the sequential action of two inner membrane proteases, leading to release of σ^E from RseA, and induction of the stress response. This mechanism of signal transduction, regulated intramembrane proteolysis, is used in transmembrane signaling pathways from bacteria to humans.