RNA-binding protein that binds to iron-responsive elements (IRES), which are stem-loop structures found in the 5'-UTR of ferritin, and delta aminolevulinic acid synthase mRNAs, and in the 3'-UTR of transferrin receptor mRNA. Binding to the IRE element in ferritin results in the repression of its mRNA translation. Binding of the protein to the transferrin receptor mRNA inhibits the degradation of this otherwise rapidly degraded mRNA. Binds 1 [4Fe-4S] cluster per subunit. [4Fe-4S]-binding affects RNA-binding activity, thereby inhibiting activity of the protein. Interacts with RBCK1 only in iron-rich conditions. Interacts (when associated with the 4Fe-4S) with FBXL5 (By similarity). Interacts with CIAO1 and CIAO2A (By similarity). Ubiquitously expressed in rat tissues, the highest amounts present in skeletal muscle and heart. Ubiquitinated and degraded by the proteasome in presence of high level of iron and oxygen. Ubiquitinated by a SCF complex containing FBXL5. Upon iron and oxygen depletion FBXL5 is degraded, preventing ubiquitination and allowing its RNA-binding activity (By similarity). Belongs to the aconitase/IPM isomerase family.