Signal Transduction and Regulatory Mechanisms Involved in Control of the σ^S(RpoS) Subunit of RNA Polymerase

Abstract

SUMMARY The σS (RpoS) subunit of RNA polymerase is the master regulator of the general stress response in Escherichia coli and related bacteria. While rapidly growing cells contain very little σS, exposure to many different stress conditions results in rapid and strong σS induction. Consequently, transcription of numerous σS-dependent genes is activated, many of which encode gene products with stress-protective functions. Multiple signal integration in the control of the cellular σS level is achieved by rpoS transcriptional and translational control as well as by regulated σS proteolysis, with various stress conditions differentially affecting these levels of σS control. Thus, a reduced growth rate results in increased rpoS transcription whereas high osmolarity, low temperature, acidic pH, and some late-log-phase signals stimulate the translation of already present rpoS mRNA. In addition, carbon starvation, high osmolarity, acidic pH, and high temperature result in stabilization of σS, which, under nonstress conditions, is degraded with a half-life of one to several minutes. Important cis-regulatory determinants as well as trans-acting regulatory factors involved at all levels of σS regulation have been identified. rpoS translation is controlled by several proteins (Hfq and HU) and small regulatory RNAs that probably affect the secondary structure of rpoS mRNA. For σS proteolysis, the response regulator RssB is essential. RssB is a specific direct σS recognition factor, whose affinity for σS is modulated by phosphorylation of its receiver domain. RssB delivers σS to the ClpXP protease, where σS is unfolded and completely degraded. This review summarizes our current knowledge about the molecular functions and interactions of these components and tries to establish a framework for further research on the mode of multiple signal input into this complex regulatory system.

Shape and evolution of the fundamental niche in marine Vibrio

“…These results indicate that salinity and temperature tolerance mechanisms may be coupled at the molecular level, consistent with the findings of previous studies demonstrating that pre-exposure to osmotic stress increased the tolerance to heat stress in V. vulnificus (Rosche et al, 2005). Such coupling may result from temperature and salinity responses using common molecular pathways such as the SOS response pathway, the heat-shock response pathway and the general stress response pathway (Hengge-Aronis, 2002;Diez-Gonzalez and Kuruc, 2009). However, Rosche et al (2005) have demonstrated that the cross-protection between osmolarity and heat in V. vulnificus is independent of rpoS, the master regulator of the general stress response mechanism, and were unable to elucidate the origin of this cross-protection.…”

Stress responses and genetic variation in bacteria

“…There are more than 70 genes in the RpoS regulon, and most of them encode proteins that help the cell survive the insults encountered by non-growing cells. Thus, RpoS is considered to be a master regulator of a general stress response (reviewed in [17]). …”

Genetic and phenotypic analysis of the GacS/GacA system in the moderate halophile Halomonas anticariensis

“…One of these is the alternative sigma factor s 38 (RpoS), which plays a key role in the survival of bacteria during starvation or exposure to stress conditions and is required for the expression of many genes in the stationary growth phase (virulence factors and secondary metabolites). It may not, however, be essential for cell viability (Hengge-Aronis, 2002;Schuster et al, 2004;Venturi, 2003). A second pathway involves the intervention of the GacS/GacA TCS in the QS cascade.…”