Transcriptional regulation of high pathogenicity island iron uptake genes by YbtA

A large group of Enterobacteriaceae, including members of the genus Yersinia, produce the extracellular siderophore yersiniabactin enabling them to multiply under iron-depleted conditions. Genes, involved in yersiniabactin synthesis, transport and regulation are clustered in the high pathogenicity island (HPI). YbtA, an AraC-like transcriptional regulator, is presumed to be the central regulator of yersiniabactin production together with the ferric uptake regulator Fur. In this work, we identified the transcriptional start points of YbtA-regulated promoters of the HPI by primer extension, purified homogeneous YbtA and defined the YbtA-binding sites by DNaseI footprint analysis in ybtA, fyuA, irp6, and irp2 promoters. Besides of the anticipated pair repeats RS1 and RS2 in each promoter, we identified an additional YbtA-binding site designated RS3 in the divergently transcribed ybtA/irp6 promoter. Also, comparing ybtA/irp6 promoters of Y. enterocolitica and Y. pestis, we found that a 125-bp ERIC element insertion in the RS2 sequence of the Y. enterocolitica ybtA/irp6 promoter might increase YbtA expression, but did not affect expression of Irp6.