title: Structural changes enable start codon recognition by the eukaryotic translation initiation complex.
abstract: During eukaryotic translation initiation, initiator tRNA does not insert fully into the P decoding site on the 40S ribosomal subunit. This conformation (POUT) is compatible with scanning mRNA for the AUG start codon. Base pairing with AUG is thought to promote isomerization to a more stable conformation (PIN) that arrests scanning and promotes dissociation of eIF1 from the 40S subunit. Here, we present a cryoEM reconstruction of a yeast preinitiation complex at 4.0 Å resolution with initiator tRNA in the PIN state, prior to eIF1 release. The structure reveals stabilization of the codon-anticodon duplex by the N-terminal tail of eIF1A, changes in the structure of eIF1 likely instrumental in its subsequent release, and changes in the conformation of eIF2. The mRNA traverses the entire mRNA cleft and makes connections to the regulatory domain of eIF2?, eIF1A, and ribosomal elements that allow recognition of context nucleotides surrounding the AUG codon.
authors.affiliation: MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, UK.
authors.forename: Tanweer
authors.initials: T
authors.lastname: Hussain
authors.affiliation: MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, UK.
authors.forename: Jose L
authors.initials: JL
authors.lastname: Llácer
authors.affiliation: MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, UK.
authors.forename: Israel S
authors.initials: IS
authors.lastname: Fernández
authors.affiliation: Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Laboratory on the Mechanism and Regulation of Protein Synthesis, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Antonio
authors.initials: A
authors.lastname: Munoz
authors.affiliation: Laboratory of Gene Regulation and Development, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Pilar
authors.initials: P
authors.lastname: Martin-Marcos
authors.affiliation: MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, UK.
authors.forename: Christos G
authors.initials: CG
authors.lastname: Savva
authors.affiliation: Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Laboratory on the Mechanism and Regulation of Protein Synthesis, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Jon R
authors.initials: JR
authors.lastname: Lorsch
authors.affiliation: Laboratory of Gene Regulation and Development, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Alan G
authors.initials: AG
authors.lastname: Hinnebusch
authors.affiliation: MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, UK. Electronic address: ramak@mrc-lmb.cam.ac.uk.
authors.forename: V
authors.initials: V
authors.lastname: Ramakrishnan
mesh_terms: D001483:Base Sequence; D018387:Codon, Initiator; D020285:Cryoelectron Microscopy; D039642:Eukaryotic Initiation Factors / Q000378:metabolism*; D007716:Kluyveromyces / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010442:Peptide Chain Initiation, Translational; D012343:RNA, Transfer / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D016415:Sequence Alignment
chemical_list: D018387:Codon, Initiator; D039642:Eukaryotic Initiation Factors; D012343:RNA, Transfer