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J. Bacteriol. doi:10.1128/JB.01305-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

YtxR acts as an overriding transcriptional off switch for the Yersinia enterocolitica Ysc-Yop type 3 secretion system

Department of Microbiology, New York University School of Medicine, New York, NY 10016; and Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, UK

^* To whom correspondence should be addressed. Email: andrew.darwin{at}med.nyu.edu.

	Abstract

The Yersinia enterocolitica YtxR protein is a LysR-type transcriptional regulator that induces expression of the ytxAB locus, which encodes a putative ADP-ribosylating toxin. The ytxR and ytxAB genes are not closely linked in the Y. enterocolitica chromosome, and whereas ytxR is present in all sequenced yersinia spp., the ytxAB locus is not. These observations suggested that there might be other YtxR-regulon members besides ytxAB and prompted us to investigate co-regulated genes and gene products using transcriptional and proteomic approaches. Microarray and reverse transcription PCR analysis showed that YtxR strongly activates expression of the yts2 locus, which encodes a putative type 2 secretion system, as well as several uncharacterized genes predicted to encode extracytoplasmic proteins. Strikingly, we also discovered that during Ysc-Yop type 3 secretion system-inducing conditions, YtxR prevented the appearance of Yop proteins in the culture supernatant. Microarray and lacZ operon fusion analysis showed that this was due to specific repression of ysc-yop gene expression. YtxR was also able to repress VirF-dependent (yopE-lacZ) and (yopH-lacZ) expression in a strain lacking the virulence plasmid, which suggested a direct repression mechanism. This was supported by DNase I footprinting, which showed that YtxR interacted with the yopE and yopH control regions. Therefore, YtxR is a newly identified regulator of the ysc-yop genes that can act as an overriding off switch for this critical virulence system.