BvgA functions as both an activator and a repressor to control Bvg<superscript>i</superscript> phase expression ofbipAinBordetella pertussis.

TheBordetella bipAgene is expressed maximally when the BvgAS phosphorelay is semi-active, i.e. in the Bvg-intermediate (Bvgi) phase. We used a BvgA-FeBABE cleavage approach together with site-directed mutagenesis andbipA–lacZfusion analyses to determine precisely where BvgA-phosphate (BvgA∼P) binds at thebipApromoter and how that binding contributes to the complex transcription pattern displayed bybipA. BvgA∼P bound with high affinity and cooperatively with RNAP to sequences at thebipApromoter immediately 5′ to and overlapping those bound by RNAP to activate transcription under Bvgi phase conditions.bipAtherefore, likefhaB, appears to be similar to classical class-II promoters with regard to the mechanism by which its transcription is activated. BvgA∼P bound with relatively low affinity to sequences immediately 3′ of those bound by RNAP at thebipApromoter and this binding mediated repression ofbipAtranscription under Bvg+ phase conditions. BvgA∼P binding to these sequences occurred simultaneously, if not cooperatively, with RNAP, indicating that BvgA∼P repressesbipAexpression by inhibiting transcription initiation and/or elongation, rather than by competing with RNAP for binding. AsbipAis the first Bvgi phase gene to be characterized, and the first gene shown to be repressed by BvgA∼P directly, our results will provide a basis for comparison as additional Bvg-regulated genes are identified and characterized. [ABSTRACT FROM AUTHOR]