Upstream sequence-dependent suppression and AtxA-dependent activation of protective antigens inBacillus anthracis

Abstract

The anthrax toxin is a virulence factor produced by the bacteriumBacillus anthracis. Transcription of anthrax toxin genes is controlled by the transcription factor AtxA. Thus, AtxA is thought to be a key factor for the pathogenicity ofB. anthracis. Despite its important role inB. anthracisinfection, the molecular mechanism by which AtxA controls expression of anthrax toxin remains unclear. This study aimed to characterize the molecular mechanism of AtxA-mediated regulation of protective antigen (PA), a component of anthrax toxin encoded by thepagAgene. First, the interaction between the upstream region ofpagAand AtxA was evaluated in vivo by constructing a transcriptional fusion of the upstream region with an auxotrophic marker. The results showed that (i) the upstream region ofpagAsuppressed transcription of the downstream gene and (ii) AtxA recovered suppressed transcription. Second, in vitro analysis using a gel mobility shift assay was performed to evaluate binding specificity of the AtxA–DNA interaction. The result showed sequence-independent binding of AtxA to DNA. Taken together, our findings suggest that the expression of PA was suppressed by the upstream region ofpagAand that an interaction of AtxA and the upstream region releases the suppression.