Down-regulation of Porins by a Small RNA Bypasses the Essentiality of the Regulated Intramembrane Proteolysis Protease RseP inEscherichia coli

Véronique Douchin, Chantal Bohn, Philippe Bouloc
2006 Journal of Biological Chemistry  
Adaptation to extracytoplasmic stress in Escherichia coli depends on the activation of E , normally sequestered by the membrane protein RseA. E is released in response to stress through the successive RseA cleavage by DegS and the RIP protease RseP. E and proteases that free it from RseA are essential. We isolated a multicopy suppressor that alleviated RseP and DegS requirement. The suppressor encodes a novel small RNA, RseX. Its activity required the RNA-binding protein Hfq. We used the
more » ... We used the property that small RNAs are often involved in RNA-RNA interactions to capture RseX putative partners; ompA and ompC mRNA, which encode two major outer membrane proteins, were identified. RseX activity was shown to confer an Hfq-dependent coordinate OmpA and OmpC downregulation. Because RseP is shown to be no longer essential in a strain lacking OmpA and OmpC, we conclude that RseP, which is required for normal E activation, prevents toxicity due to the presence of two specific outer membrane proteins that are down-regulated by RseX. Adaptations to extracytoplasmic stress in Escherichia coli are principally controlled by activation of E , an alternative sigma factor (reviewed in Refs. 1 and 2). E governs expression of genes encoding membrane proteins, proteins involved in phospholipids, lipopolysaccharide and outer membrane biosynthesis, primary metabolism, and signal transduction (3-5). Under nonstress conditions, E is retained at the membrane by the membrane-spanning anti-sigma protein RseA, and is inactive (6, 7). RseA binds to the core RNA polymerase-binding domain of E , thereby inhibiting its assembly with the RNA polymerase (8). Upon extracytoplasmic stress, e.g. induced by ethanol or unfolded proteins (9, 10), RseA undergoes a first cleavage by the DegS protease (11-13). The RseA truncated form is then susceptible to a second protease, RseP (for regulator of E protease, formerly named YaeL), that frees E (13, 14). Further degradation of the RseA cytoplasmic part is performed by the ClpXP protease (15). E , as well as proteases DegS and RseP, which contribute to activation of the E pathway, are essential for bacterial growth (16 -18).
doi:10.1074/jbc.m600819200 pmid:16513633 fatcat:gcrlwjllcfcythj53222pgcq4y