IRP-1 binding to ferritin mRNA prevents the recruitment of the small ribosomal subunit by the cap-binding complex eIF4F.
Binding of iron regulatory proteins (IRPs) to IREs located in proximity to the cap structure of ferritin H- and L-chain mRNAs blocks ferritin synthesis by preventing the recruitment of the small ribosomal subunit to the mRNA. We have devised a novel procedure to examine the assembly of translation initiation factors (eIFs) on regulated mRNAs. Unexpectedly, we find that the cap binding complex eIF4F (comprising eIF4E, eIF4G, and eIF4A) assembles even when IRP-1 is bound to the cap-proximal IRE. This assembly is futile, because bridging interactions between eIF4F and the small ribosomal subunit cannot be established in the presence of IRP-1. Our findings provide insight into translational control by an mRNA binding protein at the level of translation initiation factors and uncover a key regulatory step in iron homeostasis.
Gene Expression Programme, European Molecular Biology Laboratory, Heidelberg Germany.
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Muckenthaler
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Gray
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Hentze
D000818:Animals; D001665:Binding Sites; D039562:Eukaryotic Initiation Factor-4F; D005293:Ferritins / Q000235:genetics*; D006801:Humans; D035941:Iron Regulatory Protein 1; D035925:Iron-Regulatory Proteins; D007506:Iron-Sulfur Proteins / Q000737:chemistry / Q000378:metabolism*; D008957:Models, Genetic; D008958:Models, Molecular; D010442:Peptide Chain Initiation, Translational; D010448:Peptide Initiation Factors / Q000737:chemistry / Q000378:metabolism*; D014176:Protein Biosynthesis; D012315:RNA Caps / Q000737:chemistry / Q000378:metabolism*; D012333:RNA, Messenger / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D011817:Rabbits; D012156:Reticulocytes / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism* / Q000648:ultrastructure
D039562:Eukaryotic Initiation Factor-4F; D035925:Iron-Regulatory Proteins; D007506:Iron-Sulfur Proteins; D010448:Peptide Initiation Factors; D012315:RNA Caps; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D005293:Ferritins; D035941:Iron Regulatory Protein 1