FIG 2.

Model showing Bvg regulation of gene expression in B. pertussis and its relationship to the RisK/RisA regulatory system (Copyright Scott Stibitz and Qing Chen). (A) In the Bvg⁺ phase, BvgA is phosphorylated by BvgS and activates the transcription of virulence factor genes (vags) and also of the bvgR gene. BvgR reduces the level of c-di-GMP in the cell, repressing the activity of the RisA transcriptional activator (which is constitutively phosphorylated by RisK in the presence of truncated RisS). (B) In the Bvg⁻ phase, BvgA is not phosphorylated and so no BvgR is produced. High levels of c-di-GMP activate phosphorylated RisA, which then activates transcription of the vir-repressed genes (vrgs).