Mechanisms of iron- and O-sensing by the [4Fe-4S] cluster of the global iron regulator RirA.

RirA is a global regulator of iron homeostasis in and related α-proteobacteria. In its [4Fe-4S] cluster-bound form it represses iron uptake by binding to IRO Box sequences upstream of RirA-regulated genes. Under low iron and/or aerobic conditions, [4Fe-4S] RirA undergoes cluster conversion/degradation to apo-RirA, which can no longer bind IRO Box sequences.