YbtA, an AraC-type regulator of the Yersinia pestis pesticin/yersiniabactin receptor.

The pesticin receptor (Psn) of Yersinia pestis confers sensitivity to the bacteriocin, pesticin, and is an integral component of an inorganic-iron-transport system that functions at 37 degrees C. Synthesis of Psn is under the control of its own promoter and is regulated by iron and probably by the presence of its cognate siderophore. We have used a psn promoter fusion with lacZ to identify cis- and trans-acting factors which affect transcription of the psn gene. As expected, expression of lacZ from this construct was iron regulated and repressed by Fur. Mutations within a putative siderophore biosynthetic gene (irp2) also decreased expression. A set of repeats adjacent to the -35 region of the psn promoter was required for maximum expression of the psn::lacZ gene. Sequence analysis of the region upstream of irp2 revealed the presence of a gene (ybtA) with homology to the AraC family of transcriptional regulators. Insertional inactivation of ybtA resulted in decreased synthesis of Psn and proteins encoded by the irp2 operon as well as decreased expression from the psn::lacZ promoter fusion, indicating that YbtA is a transcriptional activator for psn and the putative siderophore biosynthetic genes. YbtA also represses its own transcription.