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Journal of Bacteriology, December 2006, p. 8033-8043, Vol. 188, No. 23
0021-9193/06/$08.00+0     doi:10.1128/JB.01159-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

YtxR, a Conserved LysR-Like Regulator That Induces Expression of Genes Encoding a Putative ADP-Ribosyltransferase Toxin Homologue in Yersinia enterocolitica

Department of Microbiology, New York University School of Medicine, New York, New York 10016,¹ Departments of Molecular Microbiology and Pediatrics, Washington University School of Medicine, St. Louis, Missouri 63110²

Received 29 July 2006/ Accepted 8 September 2006

Yersinia enterocolitica causes human gastroenteritis, and many isolates have been classified as either "American" or "non-American" strains based on their geographic prevalence and virulence properties. In this study we describe identification of a transcriptional regulator that controls expression of the Y. enterocolitica ytxAB genes. The ytxAB genes have the potential to encode an ADP-ribosylating toxin with similarity to pertussis toxin. However, a ytxAB null mutation did not affect virulence in mice. Nevertheless, the ytxAB genes are conserved in many Y. enterocolitica strains. Interestingly, American and non-American strains have different ytxAB alleles encoding proteins that are only 50 to 60% identical. To obtain further insight into the ytxAB locus, we investigated whether it is regulated as part of a known or novel regulon. Transposon mutagenesis identified a LysR-like regulator, which we designated YtxR. Expression of ytxR from a nonnative promoter increased (ytxA-lacZ) operon fusion expression up to 35-fold. YtxR also activated expression of its own promoter. DNase I footprinting showed that a His₆-YtxR fusion protein directly interacted with the ytxA and ytxR control regions at similar distances upstream of their probable transcription initiation sites, identified by primer extension. Deletion analysis demonstrated that removal of the regions protected by His₆-YtxR in vitro eliminated YtxR-dependent induction in vivo. The ytxAB locus is not present in most Yersinia species. In contrast, ytxR is conserved in multiple Yersinia species, as well as in the closely related organisms Photorhabdus luminescens and Photorhabdus asymbiotica. These observations suggest that YtxR may play a conserved role involving regulation of other genes besides ytxAB.

Published ahead of print on 22 September 2006.