title: The joining of ribosomal subunits in eukaryotes requires eIF5B.
abstract: Initiation of eukaryotic protein synthesis begins with the ribosome separated into its 40S and 60S subunits. The 40S subunit first binds eukaryotic initiation factor (eIF) 3 and an eIF2-GTP-initiator transfer RNA ternary complex. The resulting complex requires eIF1, eIF1A, eIF4A, eIF4B and eIF4F to bind to a messenger RNA and to scan to the initiation codon. eIF5 stimulates hydrolysis of eIF2-bound GTP and eIF2 is released from the 48S complex formed at the initiation codon before it is joined by a 60S subunit to form an active 80S ribosome. Here we show that hydrolysis of eIF2-bound GTP induced by eIF5 in 48S complexes is necessary but not sufficient for the subunits to join. A second factor termed eIF5B (relative molecular mass 175,000) is essential for this process. It is a homologue of the prokaryotic initiation factor IF2 (re and, like it, mediates joining of subunits and has a ribosome-dependent GTPase activity that is essential for its function.
authors.affiliation: Department of Microbiology and Immunology, State University of New York Health Science Center at Brooklyn, 11203, USA. tpestova@netmail.hscbklyn.edu
authors.forename: T V
authors.initials: TV
authors.lastname: Pestova
authors.forename: I B
authors.initials: IB
authors.lastname: Lomakin
authors.forename: J H
authors.initials: JH
authors.lastname: Lee
authors.forename: S K
authors.initials: SK
authors.lastname: Choi
authors.forename: T E
authors.initials: TE
authors.lastname: Dever
authors.forename: C U
authors.initials: CU
authors.lastname: Hellen
mesh_terms: D000595:Amino Acid Sequence; D002384:Catalysis; D018387:Codon, Initiator; D015977:Eukaryotic Initiation Factor-1 / Q000378:metabolism; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D039621:Eukaryotic Initiation Factor-3; D040061:Eukaryotic Initiation Factor-5; D020558:GTP Phosphohydrolases / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D006165:Guanylyl Imidodiphosphate / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D008969:Molecular Sequence Data; D010442:Peptide Chain Initiation, Translational; D010448:Peptide Initiation Factors / Q000378:metabolism*; D011691:Puromycin / Q000031:analogs & derivatives* / Q000096:biosynthesis; D012333:RNA, Messenger / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism*
chemical_list: D018387:Codon, Initiator; D015977:Eukaryotic Initiation Factor-1; D015852:Eukaryotic Initiation Factor-2; D039621:Eukaryotic Initiation Factor-3; D040061:Eukaryotic Initiation Factor-5; D010448:Peptide Initiation Factors; D012333:RNA, Messenger; D011994:Recombinant Proteins; C026022:eukaryotic peptide initiation factor-1A; D006165:Guanylyl Imidodiphosphate; D011691:Puromycin; C024777:methionylpuromycin; D006160:Guanosine Triphosphate; D020558:GTP Phosphohydrolases