title: Structure of the mammalian ribosomal 43S preinitiation complex bound to the scanning factor DHX29.
abstract: Eukaryotic translation initiation begins with assembly of a 43S preinitiation complex. First, methionylated initiator methionine transfer RNA (Met-tRNAi(Met)), eukaryotic initiation factor (eIF) 2, and guanosine triphosphate form a ternary complex (TC). The TC, eIF3, eIF1, and eIF1A cooperatively bind to the 40S subunit, yielding the 43S preinitiation complex, which is ready to attach to messenger RNA (mRNA) and start scanning to the initiation codon. Scanning on structured mRNAs additionally requires DHX29, a DExH-box protein that also binds directly to the 40S subunit. Here, we present a cryo-electron microscopy structure of the mammalian DHX29-bound 43S complex at 11.6 Å resolution. It reveals that eIF2 interacts with the 40S subunit via its α subunit and supports Met-tRNAi(Met) in an unexpected P/I orientation (eP/I). The structural core of eIF3 resides on the back of the 40S subunit, establishing two principal points of contact, whereas DHX29 binds around helix 16. The structure provides insights into eukaryote-specific aspects of translation, including the mechanism of action of DHX29.
authors.affiliation: Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA.
authors.forename: Yaser
authors.initials: Y
authors.lastname: Hashem
authors.forename: Amedee
authors.initials: A
authors.lastname: des Georges
authors.forename: Vidya
authors.initials: V
authors.lastname: Dhote
authors.forename: Robert
authors.initials: R
authors.lastname: Langlois
authors.forename: Hstau Y
authors.initials: HY
authors.lastname: Liao
authors.forename: Robert A
authors.initials: RA
authors.lastname: Grassucci
authors.forename: Christopher U T
authors.initials: CU
authors.lastname: Hellen
authors.forename: Tatyana V
authors.initials: TV
authors.lastname: Pestova
authors.forename: Joachim
authors.initials: J
authors.lastname: Frank
mesh_terms: D000818:Animals; D001483:Base Sequence; D002474:Cell-Free System; D020285:Cryoelectron Microscopy; D015852:Eukaryotic Initiation Factor-2 / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D008322:Mammals / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010442:Peptide Chain Initiation, Translational; D020365:RNA Helicases / Q000737:chemistry* / Q000378:metabolism; D012335:RNA, Ribosomal / Q000737:chemistry* / Q000378:metabolism; D012337:RNA, Ribosomal, 18S / Q000737:chemistry / Q000378:metabolism; D011817:Rabbits; D012261:Ribonucleoproteins / Q000737:chemistry* / Q000378:metabolism
chemical_list: D015852:Eukaryotic Initiation Factor-2; D012335:RNA, Ribosomal; D012337:RNA, Ribosomal, 18S; D012261:Ribonucleoproteins; D020365:RNA Helicases