The CpxRA signal transduction system of Escherichia coli: Growth-related autoactivation and control of unanticipated target operons

In Escherichia coli, the CpxRA two-component signal transduction system sen ses and responds to aggregated and misfolded proteins in the bacterial enve lope. We show that CpxR-P (the phosphorylated form of the cognate response regulator) activates cpxRA expression in conjunction with RpoS, suggesting an involvement of the Cpx system in stationary-phase survival. Engagement o f the CpxRA system in functions beyond protein management is indicated by s everal putative targets identified after a genomic screening for the CpxR-P recognition consensus sequence. Direct negative control of the newly ident ified targets motABcheAW (specifying motility and chemotaxis) and tsr (enco ding the serine chemoreceptor) by CpxR-P was shown by electrophoretic mobil ity shift analysis and Northern hybridization. The results suggest that the CpxRA system plays a core role in an extensive stress response network in which the coordination of protein turnover and energy conservation may be t he unifying element.