Mechanism of competence activation by the ComRS signalling system in streptococci

Authors

  • Laetitia Fontaine,

    Corresponding author
    • Biochimie et Génétique Moléculaire Bactérienne, Institut des Sciences de la Vie, Université catholique de Louvain, Louvain-la-Neuve, Belgium
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  • Philippe Goffin,

    1. Biochimie et Génétique Moléculaire Bactérienne, Institut des Sciences de la Vie, Université catholique de Louvain, Louvain-la-Neuve, Belgium
    Current affiliation:
    1. GlaxoSmithKline Vaccines, Rixensart, Belgium
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  • Hélène Dubout,

    1. Biochimie et Génétique Moléculaire Bactérienne, Institut des Sciences de la Vie, Université catholique de Louvain, Louvain-la-Neuve, Belgium
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  • Brigitte Delplace,

    1. Biochimie et Génétique Moléculaire Bactérienne, Institut des Sciences de la Vie, Université catholique de Louvain, Louvain-la-Neuve, Belgium
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  • Alain Baulard,

    1. Centre d'Infection et d'Immunité de Lille, Institut Pasteur de Lille, Lille, France
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  • Nathalie Lecat-Guillet,

    1. Centre d'Infection et d'Immunité de Lille, Institut Pasteur de Lille, Lille, France
    Current affiliation:
    1. Institut de Génomique Fonctionnelle, UMR5203, Université Montpellier I & II, Montpellier, France
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  • Emilie Chambellon,

    1. INRA, UMR1319 MICALIS, Jouy-en-Josas, France
    2. AgroParistech, UMR1319 MICALIS, Jouy-en-Josas, France
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  • Rozenn Gardan,

    1. INRA, UMR1319 MICALIS, Jouy-en-Josas, France
    2. AgroParistech, UMR1319 MICALIS, Jouy-en-Josas, France
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  • Pascal Hols

    1. Biochimie et Génétique Moléculaire Bactérienne, Institut des Sciences de la Vie, Université catholique de Louvain, Louvain-la-Neuve, Belgium
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  • Present addresses: ; .

For correspondence. E-mail laetitia.fontaine@uclouvain.be; Tel. (+1) 32 10 473486; Fax (+1) 32 10 473109.

Summary

In many streptococci, competence for natural DNA transformation is regulated by the Rgg-type regulator ComR and the pheromone ComS, which is sensed intracellularly. We compared the ComRS systems of four model streptococcal species using in vitro and in silico approaches, to determine the mechanism of the ComRS-dependent regulation of competence. In all systems investigated, ComR was shown to be the proximal transcriptional activator of the expression of key competence genes. Efficient binding of ComR to DNA is strictly dependent on the presence of the pheromone (C-terminal ComS octapeptide), in contrast with other streptococcal Rgg-type regulators. The 20 bp palindromic ComR-box is the minimal genetic requirement for binding of ComR, and its sequence directly determines the expression level of genes under its control. Despite the apparent species-specific specialization of the ComR–ComS interaction, mutagenesis of ComS residues from Streptococcus thermophilus highlighted an unexpected permissiveness with respect to its biological activity. In agreement, heterologous ComS, and even primary sequence-unrelated, casein-derived octapeptides, were able to induce competence development in S. thermophilus. The lack of stringency of ComS sequence suggests that competence of a specific Streptococcus species may be modulated by other streptococci or by non-specific nutritive oligopeptides present in its environment.

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