DIFFERENTIAL BINDING OF BVGA TO 2 CLASSES OF VIRULENCE GENES OF BORDETELLA-PERTUSSIS DIRECTS PROMOTER SELECTIVITY BY RNA-POLYMERASE

Transcription of virulence genes of Bordetella pertussis is co-ordinat ely regulated by the BvgA and BvgS proteins, which are members of the two-component family of bacterial signal-transduction proteins. BvgS i s the transmembrane sensor and BvgA the transcriptional regulator, By gel mobility shift assays we demonstrate that phosphorylated BvgA (Bvg A approximate to P) forms distinct complexes with the filamentous haem agglutinin (P-FHA) promoter DNA at different BvgA approximate to P: DN A ratios, DNase I protection analyses show that phosphorylation of Bvg A not only enhances affinity of the protein for the binding sites of t he P-FHA and bvgP(1) promoters, but it extends significantly the bound region towards position -35 of these promoters. Conversely, a 10-fold higher amount of BvgA approximate to P is required for binding to a l arge DNA region, from -168 to -60, of the pertussis toxin (P-tox) prom oter sequence. These findings suggest that the molecular interaction o f BvgA approximate to P with the P-tox promoter is different from its interaction with the P-FHA and bvgP(1) promoters, The sigma(70) Escher ichia coil RNA polymerase (RNP) does not bind to the bvg-regulated pro moters. However, following the formation of a BvgA approximate to P-pr omoter complex, the E. coil RNP specifically recognizes and binds to t he bvg-regulated promoters, Thus, BvgA approximate to P exerts its act ion at the level of promoter recognition by directing promoter selecti vity by RNP.