Bacillus anthracis Virulence Regulator AtxA Binds Specifically to the Promoter Region.

Anthrax toxin activator (AtxA) is the master virulence gene regulator of It regulates genes on the chromosome as well as the pXO1 and pXO2 plasmids. It is not clear how AtxA regulates these genes, and direct binding of AtxA to its targets has not been shown. It has been previously suggested that AtxA and other proteins in the Mga/AtxA global transcriptional regulators family bind to the curvature of their DNA targets, although this has never been experimentally proven. Using electrophoretic mobility shift assays, we demonstrate that AtxA binds directly to the promoter region of upstream of the RNA polymerase binding site. We also demonstrate that CO appears to have no role in AtxA binding. However, phosphomimetic and phosphoablative substitutions in the hosphotransferase system (PTS) egulation omains (PRDs) do appear to influence AtxA binding and regulation. and analyses demonstrate that one of two hypothesized stem-loops located upstream of the RNA polymerase binding site in the promoter region is important for AtxA binding and regulation Our study clarifies the mechanism by which AtxA interacts with one of its targets. Anthrax toxin activator (AtxA) regulates the major virulence genes in The bacterium produces the anthrax toxins, and understanding the mechanism of toxin production may facilitate the development of therapeutics for infection. Since the discovery of AtxA 25 years ago, the mechanism by which it regulates its targets has largely remained a mystery. Here, we provide evidence that AtxA binds to the promoter region of the gene encoding the main central protective antigen (PA) component of the anthrax toxin. These data suggest that AtxA binding plays a direct role in gene regulation. Our work also assists in clarifying the role of CO in AtxA's gene regulation and provides more evidence for the role of AtxA phosphorylation in virulence gene regulation.