PDZ domains of RseP are not essential for sequential cleavage of RseA or stress‐induced σ E activation in vivo

Summary The E scherichia coli σ E extracytoplasmic stress response monitors and responds to folding stress in the cell envelope. A protease cascade directed at RseA , a membrane‐spanning anti‐σ that inhibits σ E activity, controls this critical signal‐transduction system. Stress cues activate DegS to cleave RseA ; a second cleavage by RseP releases RseA from the membrane, enabling its rapid degradation. Stress control of proteolysis requires that RseP cleavage is dependent on DegS cleavage. Recent in vitro and structural studies found that RseP cleavage requires binding of RseP PDZ ‐ C to the newly exposed C ‐terminal residue ( Val 148) of RseA , generated by DegS cleavage, explaining dependence. We tested this mechanism in vivo . Neither mutation in the putative PDZ ligand‐binding regions nor even deletion of entire RseP PDZ domains had significant effects on RseA cleavage in vivo , and the C ‐terminal residue of DegS ‐processed RseA also little affected RseA cleavage. Indeed, strains with a chromosomal rseP gene deleted for either PDZ domain and strains with a chromosomal rseA V 148 mutation grew normally and exhibited almost normal σ E activation in response to stress signals. We conclude that recognition of the cleaved amino acid by the RseP PDZ domain is not essential for sequential cleavage of RseA and σ E stress response in vivo .