Transcription of the contiguous sigB, dtxR, and galE genes in Corynebacterium diphtheriae:: Evidence for multiple transcripts and regulation by environmental factors

The iron-dependent transcriptional regulator DtxR from Corynebacterium diphtheriae is the prototype for a family of metal-dependent regulators found in diverse bacterial species. The structure of DtxR and its action as a repressor have been extensively characterized, but little is known about expression of dtxR. In the current study, we investigated transcription of dtxR as well as the sigB and galE genes located immediately upstream and downstream from dtxR, respectively. We identified two promoters that determine transcription of dtxR. The first, located upstream of sigB, appears to be controlled by an extracytoplasmic function sigma factor. The second, located in the intergenic region between sigB and dtxR, is similar to promoters used by the primary vegetative sigma factors in other actinomycete species. Using quantitative real-time assays, we demonstrated that the number of transcripts initiated upstream from sigB is affected by several environmental factors. In contrast, the presence of sodium dodecyl sulfate was the only factor tested that conclusively affects the number of transcripts initiated in the sigB-dtxR intergenic region. Additionally, we provided evidence for the existence of transcripts that contain sigB, dtxR, and galE.. Our studies provide the first quantitative transcriptional analysis of a gene encoding a DtxR family regulator and give new insights into transcriptional regulation in C. diphtheriae.