Control of extracytoplasmic stress responses by regulated intramembrane proteolysis

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E.coli σ^E is activated by extracytoplasmic stress-induced two step cleavages of the anti-σ^E protein, RseA (a type II single-spanning membrane protein). We showed that RseP (formerly YaeL), an E.coli homolog of the eukaryotic S2P protease, functions as a "RIP(regulated intramembrane proteolysis)" protease that introduces the second "intramembrane" cleavage into anti-σ^E protein (RseA) following the first cleavage on the periplasmic side by DegS. Our in vivo and in vitro results demonstrated that RseP directly catalyzes proteolysis within the transmembrane sequence of RseA. We also found that RseP can cleave transmembrane sequences of some model membrane proteins that are unrelated to RseA, provided that the transmembrane region contains residues of low helical propensity. We are now addressing the molecular mechanisms of the two-step proteolysis of RseA and its regulation using in vitro reaction system reconstituted from purified components.