The 3′ iron-response elements (IREs) in this mRNA have a stem-loop structure containing AU-rich sequences (yellow) that promote mRNA degradation. At low intracellular iron concentrations, the conformation of IRE-BP (dark green) is such that it binds to the IREs, thereby inhibiting degradation. As a result, the level of transferrin receptor increases, so that more iron can be brought into the cell.
