Role for the histone-like protein H-NS in growth phase-dependent and osmotic regulation of sigma S and many sigma S-dependent genes in Escherichia coli.
The sigma S subunit of RNA polymerase (encoded by the rpoS gene) is the master regulator in a complex regulatory network that controls stationary-phase induction and osmotic regulation of many genes in Escherichia coli. Here we demonstrate that the histone-like protein H-NS is also a component of this network, in which it functions as a global inhibitor of gene expression during the exponential phase of growth. On two-dimensional gels, at least 22 sigma S-controlled proteins show increased expression in an hns mutant. H-NS also inhibits the expression of sigma S itself by a mechanism that acts at the posttranscriptional level. Our results indicate that relief of repression by H-NS plays a role in stationary-phase induction as well as in hyperosmotic induction of rpoS translation. Whereas certain sigma S-dependent genes (e.g., osmY) are only indirectly regulated by H-NS via its role in the control of sigma S expression, others are also H-NS-regulated in a sigma S-independent manner. (For this latter class of genes, rpoS hns double mutants show higher levels of expression than mutants deficient in rpoS alone.) In addition, we demonstrate that the slow-growth phenotype of hns mutants is suppressed in hns rpoS double mutants and that many second-site suppressor mutants that spontaneously arise from hns strains carry lesions that affect the expression of sigma S.
Barth
M
M
Department of Biology, University of Konstanz, Germany.
Marschall
C
C
Muffler
A
A
Fischer
D
D
Hengge-Aronis
R
R
D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000502:physiology*; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000502:physiology*; D001483:Base Sequence; D002455:Cell Division / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D004926:Escherichia coli / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D008969:Molecular Sequence Data; D009154:Mutation; D009994:Osmolar Concentration; D012808:Sigma Factor / Q000096:biosynthesis / Q000502:physiology*
D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C031908:H-NS protein, bacteria; D012808:Sigma Factor; C069567:sigma factor KatF protein, Bacteria