A Novel Bvg-Repressed Promoter Causes

In Bordetella pertussis, the promoter Pfim3-15C for the major fimbrial subunit gene fim3 is activated by the two-component system BvgAS in the Bvg+ mode but not in the Bvg− mode. However, many transcriptional profiling studies have shown that fim3 is transcribed in the Bvg− mode even when Pfim3 is in a nonpermissive state (Pfim3-13C), suggesting the presence of a reciprocally regulated element upstream of Pfim3. Here, we provide evidence that BRP is the cause of this anomalous behavior of fim3. Although BRP effects vrg-like transcription of fim3 in the Bvg− mode, it does not lead to stable production of FIM3 fimbriae, because expression of the chaperone and usher proteins FimB and FimC occurs only in the Bvg+ mode.