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  • 1
    Language: English
    In: Nucleic acids research, April 2012, Vol.40(8), pp.3623-40
    Description: A remarkable feature of many small non-coding RNAs (sRNAs) of Escherichia coli and Salmonella is their accumulation in the stationary phase of bacterial growth. Several stress response regulators and sigma factors have been reported to direct the transcription of stationary phase-specific sRNAs, but a widely conserved sRNA gene that is controlled by the major stationary phase and stress sigma factor, σ(S) (RpoS), has remained elusive. We have studied in Salmonella the conserved SdsR sRNA, previously known as RyeB, one of the most abundant stationary phase-specific sRNAs in E. coli. Alignments of the sdsR promoter region and genetic analysis strongly suggest that this sRNA gene is selectively transcribed by σ(S). We show that SdsR down-regulates the synthesis of the major Salmonella porin OmpD by Hfq-dependent base pairing; SdsR thus represents the fourth sRNA to regulate this major outer membrane porin. Similar to the InvR, MicC and RybB sRNAs, SdsR recognizes the ompD mRNA in the coding sequence, suggesting that this mRNA may be primarily targeted downstream of the start codon. The SdsR-binding site in ompD was localized by 3'-RACE, an experimental approach that promises to be of use in predicting other sRNA-target interactions in bacteria.
    Keywords: Gene Expression Regulation, Bacterial ; Bacterial Proteins -- Metabolism ; Porins -- Biosynthesis ; RNA, Small Untranslated -- Metabolism ; Salmonella -- Genetics ; Sigma Factor -- Metabolism
    ISSN: 03051048
    E-ISSN: 1362-4962
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  • 2
    In: Molecular Microbiology, January 2007, Vol.63(1), pp.193-217
    Description: The RNA chaperone, Hfq, plays a diverse role in bacterial physiology beyond its original role as a host factor required for replication of Q RNA bacteriophage. In this study, we show that Hfq is involved in the expression and secretion of virulence factors in the facultative intracellular pathogen, . A deletion strain is highly attenuated in mice after both oral and intraperitoneal infection, and shows a severe defect in invasion of epithelial cells and a growth defect in both epithelial cells and macrophages . Surprisingly, we find that these phenotypes are largely independent of the previously reported requirement of Hfq for expression of the stationary phase sigma factor, RpoS. Our results implicate Hfq as a key regulator of multiple aspects of virulence including regulation of motility and outer membrane protein (OmpD) expression in addition to invasion and intracellular growth. These pleiotropic effects are suggested to involve a network of regulatory small non‐coding RNAs, placing Hfq at the centre of post‐transcriptional regulation of virulence gene expression in . In addition, the mutation appears to cause a chronic activation of the RpoE‐mediated envelope stress response which is likely due to a misregulation of membrane protein expression.
    Keywords: Research Articles;
    ISSN: 0950-382X
    E-ISSN: 1365-2958
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  • 3
    In: Molecular Microbiology, December 2006, Vol.62(6), pp.1674-1688
    Description: The bacterial envelope stress response (ESR) is triggered by the accumulation of misfolded outer membrane proteins (OMPs) upon envelope damage or excessive OMP synthesis, and is mediated by the alternative sigma factor, σ. Activation of the σ pathway causes a rapid downregulation of major mRNAs, which prevents further build‐up of unassembled OMPs and liberates the translocation and folding apparatus under conditions that require envelope remodelling. The factors that facilitate the rapid removal of the unusually stable mRNAs in the ESR were previously unknown. We report that in the ESR relies upon two highly conserved, σ‐controlled small non‐coding RNAs, RybB and MicA. By using a transcriptomic approach and kinetic analyses of target mRNA decay , RybB was identified as the factor that selectively accelerates the decay of multiple major mRNAs upon induction of the ESR, while MicA is proposed to facilitate rapid decay of the single mRNA. In unstressed bacterial cells, the two σ‐dependent small RNAs function within a surveillance loop to maintain envelope homeostasis and to achieve autoregulation of σ.
    Keywords: Mrna Turnover ; Envelopes ; Outer Membrane Proteins ; Kinetics ; Non-Coding RNA ; Stress ; Homeostasis ; Sigma Factor ; Translocation ; Salmonella ; RNA ; Genetics & Taxonomy;
    ISSN: 0950-382X
    E-ISSN: 1365-2958
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  • 4
    Language: English
    In: Current Opinion in Microbiology, 2006, Vol.9(6), pp.605-611
    Description: Recent systematic genome searches revealed that bacteria encode a tremendous number of small non-coding RNAs (sRNAs). Whereas most of these molecules remain of unknown function, it has become increasingly clear that many of them will act to modulate gene expression at the post-transcriptional level. Where studied in more detail, sRNAs have often been found to control the expression of outer membrane proteins (OMPs). Enterobacteria such as and are now known to encode at least eight OMP-regulating sRNAs (InvR, MicA, MicC, MicF, OmrAB, RseX and RybB). These sRNAs exert their functions under a variety of growth and stress conditions, including the σ -mediated envelope stress response. An sRNA–OMP network is emerging in which some sRNAs act specifically on a single mRNA, whereas others control multiple mRNA targets.
    Keywords: Biology
    ISSN: 1369-5274
    E-ISSN: 1879-0364
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  • 5
    In: Molecular Microbiology, March 2009, Vol.71(5), pp.1228-1238
    Description: The alternative sigma factor σ is activated by unfolded outer membrane proteins (OMPs) and plays an essential role in pathogenesis. The canonical pathway of σ activation in response to envelope stress involves sequential proteolysis of the anti‐sigma factor RseA by the PDZ proteases DegS and RseP. Here we show that σ in sv. Typhimurium can also be activated by acid stress. A σ‐deficient mutant exhibits increased susceptibility to acid pH and reduced survival in an acidified phagosomal vacuole. Acid activation of σ‐dependent gene expression is independent of the unfolded OMP signal or the DegS protease but requires processing of RseA by RseP. The RseP PDZ domain is indispensable for acid induction, suggesting that acid stress may disrupt an inhibitory interaction between RseA and the RseP PDZ domain to allow RseA proteolysis in the absence of antecedent action of DegS. These observations demonstrate a novel environmental stimulus and activation pathway for the σ regulon that appear to be critically important during –host cell interactions.
    Keywords: Membrane Proteins ; Proteolysis ; Salmonella ; Iron Compounds ; Gene Expression ; Proteases;
    ISSN: 0950-382X
    E-ISSN: 1365-2958
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  • 6
    Language: English
    In: Molecular microbiology, December 2006, Vol.62(6), pp.1674-88
    Description: The bacterial envelope stress response (ESR) is triggered by the accumulation of misfolded outer membrane proteins (OMPs) upon envelope damage or excessive OMP synthesis, and is mediated by the alternative sigma factor, sigmaE. Activation of the GE pathway causes a rapid downregulation of major omp mRNAs, which prevents further build-up of unassembled OMPs and liberates the translocation and folding apparatus under conditions that require envelope remodelling. The factors that facilitate the rapid removal of the unusually stable omp mRNAs in the ESR were previously unknown. We report that in Salmonella the ESR relies upon two highly conserved, sigmaE-controlled small non-coding RNAs, RybB and MicA. By using a transcriptomic approach and kinetic analyses of target mRNA decay in vivo, RybB was identified as the factor that selectively accelerates the decay of multiple major omp mRNAs upon induction of the ESR, while MicA is proposed to facilitate rapid decay of the single ompA mRNA. In unstressed bacterial cells, the two oE-dependent small RNAs function within a surveillance loop to maintain envelope homeostasis and to achieve autoregulation of oE.
    Keywords: Bacterial Outer Membrane Proteins -- Metabolism ; RNA, Messenger -- Metabolism ; RNA, Untranslated -- Metabolism ; Salmonella -- Metabolism ; Sigma Factor -- Metabolism
    ISSN: 0950-382X
    Source: MEDLINE/PubMed (U.S. National Library of Medicine)
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