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Nature. 2015 Sep 24;525(7570):491-5. doi: 10.1038/nature14891. Epub 2015 Sep 7.

Structure of mammalian eIF3 in the context of the 43S preinitiation complex.

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HHMI, Department of Biochemistry and Molecular Biophysics, Columbia University, New York, New York 10032, USA.
Department of Cell Biology, SUNY Downstate Medical Center, Brooklyn, New York 11203, USA.
CNRS, Proteomic Platform Strasbourg - Esplanade, Strasbourg 67084, France.
Department of Biological Sciences, Columbia University, New York, New York 10032, USA.
CNRS, Architecture et Réactivité de l'ARN, Université de Strasbourg, Strasbourg 67084, France.


During eukaryotic translation initiation, 43S complexes, comprising a 40S ribosomal subunit, initiator transfer RNA and initiation factors (eIF) 2, 3, 1 and 1A, attach to the 5'-terminal region of messenger RNA and scan along it to the initiation codon. Scanning on structured mRNAs also requires the DExH-box protein DHX29. Mammalian eIF3 contains 13 subunits and participates in nearly all steps of translation initiation. Eight subunits having PCI (proteasome, COP9 signalosome, eIF3) or MPN (Mpr1, Pad1, amino-terminal) domains constitute the structural core of eIF3, to which five peripheral subunits are flexibly linked. Here we present a cryo-electron microscopy structure of eIF3 in the context of the DHX29-bound 43S complex, showing the PCI/MPN core at ∼6 Å resolution. It reveals the organization of the individual subunits and their interactions with components of the 43S complex. We were able to build near-complete polyalanine-level models of the eIF3 PCI/MPN core and of two peripheral subunits. The implications for understanding mRNA ribosomal attachment and scanning are discussed.

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