FIGURE 8.

Model for control of irr gene transcription by iron and manganese via Irr and Fur, respectively. The binding of Irr and Fur on their respective binding sites are shown as a function of the iron and manganese conditions. Fur binds DNA to repress transcription only when Fur is complexed with Mn²⁺. However, Mn²⁺-complexed Fur cannot bind the irr promoter when Irr is bound, which occurs under low iron conditions, resulting in derepression of the irr gene. The broken line denotes degraded Irr.