Figure 1

(a) Organization of a canonical TA system (after [49]). (b) In the presence of the operon (mother cell and right daughter cell), the antitoxin (blue) is produced together with the poison (red) and the former neutralizes the latter; the transcription of the system is auto-regulated by the binding of the antitoxin (and/or the [antitoxin+toxin] complex) to the promoter region (yellow) of the operon. In the absence of the TA operon, the unstable antitoxin is degraded by a protease (green) and the poison can exert its toxicity on an essential intracellular host target.