A network of eIF2? interactions with eIF1 and Met-tRNAi promotes accurate start codon selection by the translation preinitiation complex.

In translation initiation, a 43S preinitiation complex (PIC) containing eIF1 and a ternary complex (TC) of GTP-bound eIF2 and Met-RNAi scans the mRNA for the start codon. AUG recognition triggers eIF1 release and rearrangement from an open PIC conformation to a closed state with more tightly-bound Met-tRNAi (PIN state). Cryo-EM ...
models reveal eIF2? contacts with eIF1 and Met-tRNAi exclusive to the open complex that should destabilize the closed state. eIF2? or eIF1 substitutions disrupting these contacts increase initiation at UUG codons, and compound substitutions also derepress translation of GCN4, indicating slower TC recruitment. The latter substitutions slow TC loading while stabilizing TC binding at UUG codons in reconstituted PICs, indicating a destabilized open complex and shift to the closed/PIN state. An eIF1 substitution that should strengthen the eIF2?:eIF1 interface has the opposite genetic and biochemical phenotypes. eIF2? is also predicted to restrict Met-tRNAi movement into the closed/PIN state, and substitutions that should diminish this clash increase UUG initiation in vivo and stabilize Met-tRNAi binding at UUG codons in vitro with little effect on TC loading. Thus, eIF2? anchors eIF1 and TC to the open complex, enhancing PIC assembly and scanning, while impeding rearrangement to the closed conformation at non-AUG codons.
Mesh Terms:
Basic-Leucine Zipper Transcription Factors, Codon, Initiator, Cryoelectron Microscopy, Eukaryotic Initiation Factor-1, Eukaryotic Initiation Factor-2B, Peptide Chain Initiation, Translational, Protein Biosynthesis, RNA, Transfer, Met, Saccharomyces cerevisiae, Saccharomyces cerevisiae Proteins, Ternary Complex Factors
Nucleic Acids Res.
Date: Dec. 18, 2018
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