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 t ranslational level through interaction between a stem-loop structure, the iron-responsive element (IRE), located in the 5'-untranslated regi on (5'-UTR) of ferritin mRNAs, and a protein, the iron regulatory prot ein (IRP). The role of IRE secondary structure in translational regula tion of ferritin synthesis was explored by introducing ferritin constr ucts containing mutations in the IRE into Rat-2 fibroblasts, Our in vi vo studies demonstrate that size and sequence of the loop within the I RE and the distance and/or spatial relationship of this loop to the bu lged nucleotide region closest to the loop must be preserved in:order to observe iron-dependent translation of ferritin mRNA, In contrast, c hanges in nucleotide sequence of the upper stem can be introduced with out affecting translational regulation in vivo,as long as a stem can b e 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 or der to maintain iron-dependent regulation of translation.