title: Regulation of acid resistance by connectors of two-component signal transduction systems in Escherichia coli.
abstract: Two-component signal transduction systems (TCSs), utilized extensively by bacteria and archaea, are involved in the rapid adaptation of the organisms to fluctuating environments. A typical TCS transduces the signal by a phosphorelay between the sensor histidine kinase and its cognate response regulator. Recently, small-sized proteins that link TCSs have been reported and are called "connectors." Their physiological roles, however, have remained elusive. SafA (sensor associating factor A) (formerly B1500), a small (65-amino-acid [65-aa]) membrane protein, is among such connectors and links Escherichia coli TCSs EvgS/EvgA and PhoQ/PhoP. Since the activation of the EvgS/EvgA system induces acid resistance, we examined whether the SafA-activated PhoQ/PhoP system is also involved in the acid resistance induced by EvgS/EvgA. Using a constitutively active evgS1 mutant for the activation of EvgS/EvgA, we found that SafA, PhoQ, and PhoP all contributed to the acid resistance phenotype. Moreover, EvgS/EvgA activation resulted in the accumulation of cellular RpoS in the exponential-phase cells in a SafA-, PhoQ-, and PhoP-dependent manner. This RpoS accumulation was caused by another connector, IraM, expression of which was induced by the activation of the PhoQ/PhoP system, thus preventing RpoS degradation by trapping response regulator RssB. Acid resistance assays demonstrated that IraM also participated in the EvgS/EvgA-induced acid resistance. Therefore, we propose a model of a signal transduction cascade proceeding from EvgS/EvgA to PhoQ/PhoP and then to RssB (connected by SafA and IraM) and discuss its contribution to the acid resistance phenotype.
authors.affiliation: Department of Bioscience, Graduate School of Agriculture, Kinki University, Nakamachi, Nara 631-8505, Japan. utsumi@nara.kindai.ac.jp
authors.forename: Yoko
authors.initials: Y
authors.lastname: Eguchi
authors.forename: Eiji
authors.initials: E
authors.lastname: Ishii
authors.forename: Kensuke
authors.initials: K
authors.lastname: Hata
authors.forename: Ryutaro
authors.initials: R
authors.lastname: Utsumi
mesh_terms: D000143:Acids / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial / Q000235:genetics / Q000502:physiology; D004926:Escherichia coli / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D000143:Acids; D029968:Escherichia coli Proteins