Differential binding of BvgA to two classes of virulence genes of Bordetella pertussis directs promoter selectivity by RNA polymerase.

Transcription of virulence genes of Bordetella pertussis is co-ordinately regulated by the BvgA and BvgS proteins, which are members of the two-component family of bacterial signal-transduction proteins. BvgS is the transmembrane sensor and BvgA the transcriptional regulator. By gel mobility shift assays we demonstrate that phosphorylated BvgA (BvgA approximately P) forms distinct complexes with the filamentous haemagglutinin (PFHA) promoter DNA at different BvgA approximately P: DNA ratios. DNase I protection analyses show that phosphorylation of BvgA not only enhances affinity of the protein for the binding sites of the PFHA and bvgP1 promoters, but it extends significantly the bound region towards position -35 of these promoters. Conversely, a 10-fold higher amount of BvgA approximately P is required for binding to a large DNA region, from -168 to -60, of the pertussis toxin (Ptox) promoter sequence. These findings suggest that the molecular interaction of BvgA approximately P with the Ptox promoter is different from its interaction with the PFHA and bvgP1 promoters. The sigma 70 Escherichia coli RNA polymerase (RNP) does not bind to the bvg-regulated promoters. However, following the formation of a BvgA approximately P-promoter complex, the E. coli RNP specifically recognizes and binds to the bvg-regulated promoters. Thus, BvgA approximately P exerts its action at the level of promoter recognition by directing promoter selectivity by RNP.