FIG 5.

Model of ExoR regulation. Under neutral environmental conditions, ExoR represses the sensor kinase ChvG by direct interaction, preventing the phosphorylation cascade to ChvI and the regulation, both repression and activation, of ChvI-regulated genes. Under acidic environmental conditions, ExoR is cleaved by a periplasmic protease, relieving its inhibition of ChvG. This allows ChvG autophosphorylation and transfer of phosphate to ChvI, which then can bind DNA and regulate its target promoters. The T-bar line represents repression, the straight arrow represents activation, and the wavy arrow represents changes in these functional categories in both directions.