Figure 8. Proposed model for negative autoregulation caused by Rv2827c binding to the four rv2827c–rv2826c promoter inverted repeats.

(A) Schematic representation of the putative rv2827c–rv2826c type IV toxin-antitoxin system. Model shows both rv2827c and rv2826c being translated into the antagonistic antitoxin and toxin protein pair, respectively. The antitoxin, Rv2827c, has a second function and binds to the rv2827c–rv2826c promoter, negatively autoregulating the operon. (B) An order of binding is created by the distinct affinity values for the inverted repeats represented in the sequence level cartoon, calculated from individual IR data gathered using mutant probes (Figures 4C,D and 5C, D). Rv2827c binds negatively co-operatively, initially to IR1 (0.0205 µM) followed by IR4 (0.121 µM), IR2 (0.862 µM) and finally IR3 (11.0 µM).