ROLE OF RNA SECONDARY STRUCTURE OF THE IRON-RESPONSIVE ELEMENT IN TRANSLATIONAL REGULATION OF FERRITIN SYNTHESIS

Iron regulates synthesis of the iron storage protein ferritin at the translational level through interaction between a stem-loop structure, the iron-responsive element (IRE), located in the 5'-untranslated region (5'-UTR) of ferritin mRNAs, and a protein, the iron regulatory protein (IRP). The role of IRE secondary structure in translational regulation of ferritin synthesis was explored by introducing ferritin constructs containing mutations in the IRE into Rat-2 fibroblasts, Our in vivo studies demonstrate that size and sequence of the loop within the IRE and the distance and/or spatial relationship of this loop to the bulged nucleotide region closest to the loop must be preserved in:order to observe iron-dependent translation of ferritin mRNA, In contrast, changes in nucleotide sequence of the upper stem can be introduced without affecting translational regulation in vivo,as long as a stem can be formed. Our in vivo results suggest that only a very small variation in the affinity of interaction of IRP with IRE can be tolerated in order to maintain iron-dependent regulation of translation.