| Yersinia enterocolitica, an enteric pathogen that causes gastroenteritis, is the species of Yersinia most commonly isolated from humans. This work describes the identification and characterization of a transcriptional regulator of the ytxAB operon, which may encode the first example of an ADP-Ribosylating toxin of this species. To better understand the role of this locus we investigated its regulation. Transposon mutagenesis identified a LysR-like regulator, which we named YtxR. Expression of ytxR from a non-native promoter induced both ytxA and ytxR expression. DNAseI footprinting indicated that regulation is a result of direct binding of YtxR to these control regions. Deletion of the protected regions abolished YtxR-dependent induction of both genes in vivo. YtxR is conserved in Yersinia, Photorhabdus, and Proteus species. In contrast, the ytxAB genes are only found in two species of Yersiniae. This suggests that YtxR regulates additional genes. Consistent with this, microarray analysis revealed that YtxR positively regulates a novel group of genes encoding putative extracytoplasmic proteins as well as the Yts2 type-2 secretion system. To investigate the significance of this finding secreted proteins were analyzed. SDS-PAGE of culture supernatants showed that secretion of macrophage disabling Yop proteins was abolished by ytxR over-expression. Further investigation by analysis of ysc/yop-lacZ operon fusions indicated that over-expression of ytxR resulted in complete transcriptional repression of these genes. DNAseI footprinting assays showed YtxR directly repressed yopH and yopE expression by binding to their respective control regions. The Ysc-Yop system is essential for Yersinia virulence through evasion of innate immunity in lymphoid tissues. It is the most well-studied and important virulence system of Yersiniae. YtxR represents a highly specific and novel mechanism of repression of the anti-host weaponry of the Ysc-Yop system. |
