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Research

The Crl-RpoS Regulon of Escherichia coli^{* ,S}

Cécile Lelong^,, Kryssia Aguiluz, Sylvie Luche^¶, Lauriane Kuhn^||, Jérôme Garin^||, Thierry Rabilloud^¶ and Johannes Geiselmann

From the Laboratoire Adaptation et Pathogénie des Microorganismes, Institut Jean Roget, Campus de la Merci, Université Joseph Fourier, BP170, 38042 Grenoble cedex 9, France and ^¶ Commissariat à l'Energie Atomique (CEA), Institut de Recherches en Technologies et Sciences pour le Vivant-Laboratoire d'Etude de la Dynamique des Protéomes, INSERM 548 and ^|| INSERM/CEA/Université Joseph Fourier UNIT-M 201, Laboratoire de Chimie des Protéines, CEA Grenoble, 17 avenue des Martyrs, 38054 Grenoble, France

The RpoS subunit of RNA polymerase controls the expression of numerous genes involved in stationary phase and in response to different stress conditions. The regulatory protein Crl increases the activity of RpoS by direct interaction with the RpoS holoenzyme. To define the extent of the Crl regulon, we used two-dimensional SDS-PAGE to measure the role of Crl in regulating the expression of the Escherichia coliproteome in stationary phase at 30 °C. By comparing the proteome of four strains (wild type, crl^–, rpoS^–, and crl^–rpoS^–), we observed that the intensity of 74 spots was modified in at least one mutant context. 62 spots were identified by mass spectrometry and correspond to 40 distinct proteins. They were classified in four main categories: DNA metabolism, central metabolism, response to environmental modifications, and miscellaneous. Three proteins were specifically involved in quorum sensing: TnaA (the tryptophanase that converts tryptophan to indole), WrbA (Trp repressor-binding protein), and YgaG (homologous to LuxS, autoinducer-2 synthase). Because little is known about the regulation of Crl expression, we investigated the influence of diffusible molecules on the expression of Crl. Using Western blotting experiments, we showed that, at 30 °C, a diffusible molecule(s) produced during the transition phase between the exponential and stationary phases induces a premature expression of Crl. Indole was tested as one of the potential candidates: at 37 °C, it is present in the extracellular medium at a constant concentration, but at 30 °C, its concentration peaks during the transition phase. When indole was added to the culture medium, it also induced prematurely the expression of Crl at both the transcriptional and translational levels in a Crl-dependent manner. Crl may thus be considered a new environmental sensor via the indole concentration.