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.
Publication types
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Amino Acid Sequence
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Catalysis
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Codon, Initiator
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Eukaryotic Initiation Factor-1 / metabolism
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Eukaryotic Initiation Factor-2 / metabolism
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Eukaryotic Initiation Factor-3
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Eukaryotic Initiation Factor-5
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GTP Phosphohydrolases / metabolism
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Guanosine Triphosphate / metabolism
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Guanylyl Imidodiphosphate / metabolism
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Humans
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Hydrolysis
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Molecular Sequence Data
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Peptide Chain Initiation, Translational*
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Peptide Initiation Factors / metabolism*
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Puromycin / analogs & derivatives*
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Puromycin / biosynthesis
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RNA, Messenger / metabolism
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Recombinant Proteins / metabolism
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Ribosomes / metabolism*
Substances
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Codon, Initiator
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Eukaryotic Initiation Factor-1
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Eukaryotic Initiation Factor-2
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Eukaryotic Initiation Factor-3
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Eukaryotic Initiation Factor-5
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Peptide Initiation Factors
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RNA, Messenger
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Recombinant Proteins
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eukaryotic peptide initiation factor-1A
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Guanylyl Imidodiphosphate
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Puromycin
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methionylpuromycin
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Guanosine Triphosphate
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GTP Phosphohydrolases