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Repressor activity of the RpoS/σS-dependent RNA polymerase requires DNA binding.

Corinne Lévi-Meyrueis1, Véronique Monteil2, Odile Sismeiro3

  • 1Institut Pasteur, Laboratoire Systèmes Macromoléculaires et Signalisation, Département de Microbiologie, rue du Docteur Roux, 75015 Paris, France CNRS ERL3526, rue du Docteur Roux, 75015 Paris, France Université Paris Sud XI, 15, rue Georges Clémenceau, 91405 Orsay Cedex, France.

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The sigma S (σ(S)) protein

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Area of Science:

  • Microbiology
  • Molecular Biology
  • Bacterial Genetics

Background:

  • RpoS (σ(S)) is a key sigma factor in Gram-negative bacteria, regulating stationary phase genes and adaptive traits like stress resistance, biofilm formation, and virulence.
  • Negative regulation by σ(S) is hypothesized to occur through competition with other sigma factors for core RNA polymerase (RNAP).
  • The precise mechanisms of σ(S)-mediated gene repression remain incompletely understood.

Purpose of the Study:

  • To investigate whether σ(S) binding to core RNAP alone, without DNA binding, causes significant gene downregulation.
  • To elucidate the role of σ(S) DNA binding in negative transcriptional regulation.

Main Methods:

  • Characterization of an rpoS mutant in Salmonella enterica serovar Typhimurium.
  • The mutant produced a σ(S) protein capable of forming the Eσ(S) complex but unable to bind promoter DNA.
  • Genome-wide expression profiling and physiological assays were employed.

Main Results:

  • The characterized rpoS mutant exhibited defects in negative regulation, demonstrating that σ(S) repression requires DNA binding.
  • Gene expression profiling revealed significant alterations in the expression of various genes.
  • Physiological assays confirmed the functional impact of the observed regulatory defects.

Conclusions:

  • σ(S)-mediated gene repression necessitates its direct binding to promoter DNA.
  • Competition for promoter DNA binding by sigma factors is a significant mechanism for Eσ(S)-mediated gene repression.
  • The specific mechanisms of repression are gene and condition-dependent, as exemplified by the succinate dehydrogenase operon.