title: Identification of conserved, RpoS-dependent stationary-phase genes of Escherichia coli.
abstract: During entry into stationary phase, many free-living, gram-negative bacteria express genes that impart cellular resistance to environmental stresses, such as oxidative stress and osmotic stress. Many genes that are required for stationary-phase adaptation are controlled by RpoS, a conserved alternative sigma factor, whose expression is, in turn, controlled by many factors. To better understand the numbers and types of genes dependent upon RpoS, we employed a genetic screen to isolate more than 100 independent RpoS-dependent gene fusions from a bank of several thousand mutants harboring random, independent promoter-lacZ operon fusion mutations. Dependence on RpoS varied from 2-fold to over 100-fold. The expression of all fusion mutations was normal in an rpoS/rpoS+ merodiploid (rpoS background transformed with an rpoS-containing plasmid). Surprisingly, the expression of many RpoS-dependent genes was growth phase dependent, albeit at lower levels, even in an rpoS background, suggesting that other growth-phase-dependent regulatory mechanisms, in addition to RpoS, may control postexponential gene expression. These results are consistent with the idea that many growth-phase-regulated functions in Escherichia coli do not require RpoS for expression. The identities of the 10 most highly RpoS-dependent fusions identified in this study were determined by DNA sequence analysis. Three of the mutations mapped to otsA, katE, ecnB, and osmY-genes that have been previously shown by others to be highly RpoS dependent. The six remaining highly-RpoS-dependent fusion mutations were located in other genes, namely, gabP, yhiUV, o371, o381, f186, and o215.
authors.affiliation: Department of Biology, McMaster University, Hamilton, Ontario L8S 4K1, Canada. schell@mcmaster.ca
authors.forename: H E
authors.initials: HE
authors.lastname: Schellhorn
authors.forename: J P
authors.initials: JP
authors.lastname: Audia
authors.forename: L I
authors.initials: LI
authors.lastname: Wei
authors.forename: L
authors.initials: L
authors.lastname: Chang
mesh_terms: D019677:Artificial Gene Fusion; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D001483:Base Sequence; D017931:DNA Primers / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D018507:Gene Expression Regulation, Developmental; D005798:Genes, Bacterial; D007763:Lac Operon; D009154:Mutation; D011401:Promoter Regions, Genetic; D012329:RNA, Bacterial / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics; D012808:Sigma Factor / Q000235:genetics* / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D017931:DNA Primers; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D012329:RNA, Bacterial; D012333:RNA, Messenger; D012097:Repressor Proteins; C112239:Rsd protein, E coli; D012808:Sigma Factor; C069567:sigma factor KatF protein, Bacteria