FIGURE 6.

Schematic model showing newly proposed mechanism of activation of espACD expression by simultaneous binding of PhoP and EspR. It should be noted that EspR upon binding to DNA has been suggested to form hairpin-like structures (40). Here, we propose that the additional stability of the higher order complex is perhaps attributable to protein-protein interaction between PhoP and EspR. The proteins remain bound to their target sites away from the transcription start site allowing RNA polymerase to initiate transcription. Notably, EspA and EspC proteins are themselves substrates for the ESX-1 secretion system co-secreting ESA-6 and CFP-10.