Defining the disulphide stress response in Streptomyces coelicolor A3(2): identification of the σR regulon

Authors

  • Mark S. B. Paget,

    Corresponding author
    1. Department of Molecular Microbiology, John Innes Centre, Colney, Norwich NR4 7UH, UK.
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    • Present address: School of Biological Sciences, University of Sussex, Brighton BN1 9QG, UK.

  • Virginie Molle,

    1. Department of Molecular Microbiology, John Innes Centre, Colney, Norwich NR4 7UH, UK.
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    • Present address: Department of Molecular and Cellular Biology, The Biological Laboratories, Harvard University, Cambridge, MA 02138, USA.

  • Gerald Cohen,

    1. Department of Molecular Microbiology and Biotechnology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv 69978, Israel.
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  • Yair Aharonowitz,

    1. Department of Molecular Microbiology and Biotechnology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv 69978, Israel.
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  • Mark J. Buttner

    1. Department of Molecular Microbiology, John Innes Centre, Colney, Norwich NR4 7UH, UK.
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Abstract

In the Gram-positive, antibiotic-producing bacterium Streptomyces coelicolor A3(2), the thiol-disulphide status of the hyphae is controlled by a novel regulatory system consisting of a sigma factor, σR, and its cognate anti-sigma factor, RsrA. Oxidative stress induces intramolecular disulphide bond formation in RsrA, which causes it to lose affinity for σR, thereby releasing σR to activate transcription of the thioredoxin operon, trxBA. Here, we exploit a preliminary consensus sequence for σR target promoters to identify 27 new σR target genes and operons, thereby defining the global response to disulphide stress in this organism. Target genes related to thiol metabolism encode a second thioredoxin (TrxC), a glutaredoxin-like protein and enzymes involved in the biosynthesis of the low-molecular-weight thiol-containing compounds cysteine and molybdopterin. In addition, the level of the major actinomycete thiol buffer, mycothiol, was fourfold lower in a sigR null mutant, although no candidate mycothiol biosynthetic genes were identified among the σR targets. Three σR target genes encode ribosome-associated products (ribosomal subunit L31, ppGpp synthetase and tmRNA), suggesting that the translational machinery is modified by disulphide stress. The product of another σR target gene was found to be a novel RNA polymerase-associated protein, RbpA, suggesting that the transcriptional machinery may also be modified in response to disulphide stress. We present DNA sequence evidence that many of the targets identified in S. coelicolor are also under the control of the σR homologue in the actinomycete pathogen Mycobacterium tuberculosis.

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