Efficient translation of the RpoS sigma factor in Salmonella typhimurium requires host factor I, an RNA-binding protein encoded by the hfq gene.
The RpoS transcription factor (also called sigma Sor sigma 38) is required for the expression of a number of stationary-phase and osmotically inducible genes in Escherichia coli. RpoS is also a virulence factor for several pathogenic bacteria, including Salmonella typhimurium. The activity of RpoS is regulated in response to several different signals, at the transcriptional and translational levels as well as by proteolysis. Here we report that host factor I (HF-I), the product of the hfq gene, is required for efficient expression of rpoS in S. typhimurium. HF-I is a small, heat-stable, site-specific RNA-binding protein originally characterized for its role in replication of the RNA bacteriophage Q beta of E. coli. Its role in the uninfected bacterial cell has previously been unknown. Assays of Beta-galactosidase in strains with rpoS-lac fusions, Western blot (immunoblot) analysis, and pulse-labeling and immunoprecipitation of both fusion proteins and native RpoS show that an S. typhimurium hfq mutant has a four- to sevenfold reduction in expression of rpoS that is attributable primarily to a defect in translation. These results add a new level of complexity to the regulation of RpoS activity.
Brown
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L
Department of Microbiology and Immunology, West Virginia University Health Sciences Center, Morgantown, West Virginia 26506, USA.
Elliott
T
T
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D015870:Gene Expression; D015964:Gene Expression Regulation, Bacterial; D035001:Host Factor 1 Protein; D034982:Integration Host Factors; D007763:Lac Operon; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D011233:Precipitin Tests; D014176:Protein Biosynthesis; D016601:RNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000235:genetics; D012486:Salmonella typhimurium / Q000235:genetics* / Q000378:metabolism; D012808:Sigma Factor / Q000235:genetics* / Q000378:metabolism
D001426:Bacterial Proteins; D002352:Carrier Proteins; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D035001:Host Factor 1 Protein; D034982:Integration Host Factors; D016601:RNA-Binding Proteins; D011993:Recombinant Fusion Proteins; D012808:Sigma Factor; C440502:integration host factor, E coli; C069567:sigma factor KatF protein, Bacteria