FIGURE 5.

Transcription regulation of the E. coli hicAB module. The inverse genetic organization of this module requires a dual mode of regulation via two promoter/operator sites. (a) An upstream promoter is activated by Sxy (red) and induces transcription of both toxin and antitoxin. (b) A secondary promoter is recognized by the antitoxin HicB, which acts as a repressor of the hicAB operon. Binding of the toxin HicA to HicB abolishes DNA binding and activates transcription from this secondary promoter. The resulting transcript solely allows the production of HicB antitoxin