Figure 1.

Iron responsive elements and iron regulatory proteins. (A) Consensus sequence of the eukaryotic IRE (1). (B) IREs are stem-loop structures located in 5′ or 3′ UTRs (shown in gray) of mRNAs encoding proteins involved in iron metabolism. If the IRE is located in the 5′ UTR, binding of IRP (black crescents) inhibits initiation of translation and the level of the protein product decreases. If the IRE is located in the 3′ UTR, binding of IRP protects the mRNA against degradation and the level of the protein increases. In the presence of iron, IRPs are converted to a form that is inactive for RNA binding but may have aconitase enzyme activity. The cube signifies a 4Fe-4S cluster that is essential for aconitase enzyme activity.