The cellular concentration of the sigma S subunit of RNA polymerase in Escherichia coli is controlled at the levels of transcription, translation, and protein stability.
The second vegetative sigma factor sigma S (encoded by the rpoS gene) is the master regulator in a complex regulatory network that governs the expression of many stationary phase-induced and osmotically regulated genes in Escherichia coli. Using a combination of gene-fusion technology and quantitative immunoblot, pulse-labeling, and immunoprecipitation analyses, we demonstrate here that rpoS/sigma S expression is not only transcriptionally controlled, but is also extensively regulated at the levels of translation and protein stability. rpoS transcription is inversely correlated with growth rate and is negatively controlled by cAMP-CRP. In complex medium rpoS transcription is stimulated during entry into stationary phase, whereas in minimal media, it is not significantly induced. rpoS translation is stimulated during transition into stationary phase as well as by an increase in medium osmolarity. A model involving mRNA secondary structure is suggested for this novel type of post-transcriptional growth phase-dependent and osmotic regulation. Furthermore, sigma S is a highly unstable protein in exponentially growing cells (with a half-life of 1.4 min), that is stabilized at the onset of starvation. When cells are grown in minimal glucose medium, translational induction and sigma S stabilization occur in a temporal order with the former being stimulated already in late exponential phase and the latter taking place at the onset of starvation. Although sigma S does not control its own transcription, it is apparently indirectly involved in a negative feedback control that operates on the post-transcriptional level. Our analysis also indicates that at least five different signals [cAMP, a growth rate-related signal (ppGpp?), a cell density signal, an osmotic signal, and a starvation signal] are involved in the control of all these processes that regulate rpoS/sigma S expression.
Lange
R
R
Department of Biology, University of Konstanz, Germany.
Hengge-Aronis
R
R
D001483:Base Sequence; D000242:Cyclic AMP / Q000378:metabolism; D017931:DNA Primers; D012321:DNA-Directed RNA Polymerases / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D004795:Enzyme Stability; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D015964:Gene Expression Regulation, Bacterial; D015971:Gene Expression Regulation, Enzymologic; D005798:Genes, Bacterial; D005838:Genotype; D007700:Kinetics; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D014176:Protein Biosynthesis; D012329:RNA, Bacterial / Q000737:chemistry / Q000378:metabolism; D012333:RNA, Messenger / Q000737:chemistry / Q000378:metabolism; D011953:Receptors, Cyclic AMP / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D014158:Transcription, Genetic; D001616:beta-Galactosidase / Q000096:biosynthesis
D017931:DNA Primers; D046911:Macromolecular Substances; D012329:RNA, Bacterial; D012333:RNA, Messenger; D011953:Receptors, Cyclic AMP; D011993:Recombinant Fusion Proteins; D000242:Cyclic AMP; D012321:DNA-Directed RNA Polymerases; D001616:beta-Galactosidase