The RNA-binding protein HF-I, known as a host factor for phage Qbeta RNA replication, is essential for rpoS translation in Escherichia coli.
The rpoS-encoded sigma(S) subunit of RNA polymerase in Escherichia coli is a global regulatory factor involved in several stress responses. Mainly because of increased rpoS translation and stabilization of sigma(S), which in nonstressed cells is a highly unstable protein, the cellular sigma(S) content increases during entry into stationary phase and in response to hyperosmolarity. Here, we identify the hfq-encoded RNA-binding protein HF-I, which has been known previously only as a host factor for the replication of phage Qbeta RNA, as an essential factor for rpoS translation. An hfq null mutant exhibits strongly reduced sigma(S) levels under all conditions tested and is deficient for growth phase-related and osmotic induction of sigma(S). Using a combination of gene fusion analysis and pulse-chase experiments, we demonstrate that the hfq mutant is specifically impaired in rpoS translation. We also present evidence that the H-NS protein, which has been shown to affect rpoS translation, acts in the same regulatory pathway as HF-I at a position upstream of HF-I or in conjunction with HF-I. In addition, we show that expression and heat induction of the heat shock sigma factor sigma(32) (encoded by rpoH) is not dependent on HF-I, although rpoH and rpoS are both subject to translational regulation probably mediated by changes in mRNA secondary structure. HF-I is the first factor known to be specifically involved in rpoS translation, and this role is the first cellular function to be identified for this abundant ribosome-associated RNA-binding protein in E. coli.
Muffler
A
A
Department of Biology, University of Konstanz, Germany.
Fischer
D
D
Hengge-Aronis
R
R
D017908:Allolevivirus / Q000502:physiology; D001425:Bacterial Outer Membrane Proteins / Q000502:physiology; D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000502:physiology*; D002352:Carrier Proteins / Q000235:genetics; D004268:DNA-Binding Proteins / Q000502:physiology; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D006360:Heat-Shock Proteins / Q000096:biosynthesis; D018869:Heat-Shock Response; D035001:Host Factor 1 Protein; D034982:Integration Host Factors; D009154:Mutation; D014176:Protein Biosynthesis / Q000502:physiology*; D012367:RNA, Viral / Q000096:biosynthesis; D016601:RNA-Binding Proteins / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D012808:Sigma Factor / Q000096:biosynthesis* / Q000235:genetics; D014157:Transcription Factors; D014882:Water-Electrolyte Balance; D001616:beta-Galactosidase / Q000096:biosynthesis
D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C031908:H-NS protein, bacteria; D006360:Heat-Shock Proteins; C087373:Hfq protein, E coli; D035001:Host Factor 1 Protein; D034982:Integration Host Factors; D012367:RNA, Viral; D016601:RNA-Binding Proteins; D011993:Recombinant Fusion Proteins; D012808:Sigma Factor; D014157:Transcription Factors; C069774:heat-shock sigma factor 32; C440502:integration host factor, E coli; C069567:sigma factor KatF protein, Bacteria; D001616:beta-Galactosidase