Eukaryotic initiation factor 5 from calf liver is a single polypeptide chain protein of M(r) = 62,000

P. Raychaudhuri, A. Chaudhuri, U. Maitra

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20 Scopus citations

Abstract

Eukaryotic initiation factor 5 (eIF-5), which specifically catalyzes the joining of a 60 S ribosomal subunit to a 40 S initiation complex to form a functional 80 S initiation complex, has been purified from ribosomal salt wash proteins of calf liver. The purified factor exhibits only one polypeptide band of M(r) = 62,000 following electrophoresis in 10% polyacrylamide gels in the presence of sodium dodecyl sulfate. The native protein has a sedimentation coefficient of 4.2 S and a Stokes radius of 33 Å which is consistent with eIF-5 being a monomeric protein of M(r) = 58,000-62,000. Less pure preparations of eIF-5 elute in gel filtration columns with an apparent M(r) of 160,000-180,000 presumably due to association of eIF-5 with other high molecular weight proteins since eIF-5 activity present in such preparations can also be shown by gel electrophoretic separation under denaturing conditions to be associated with a 62,000-dalton protein. Furthermore, eIF-5 purified from calf liver extracts with or without a number of protease inhibitors is indistinguishable with regard to molecular weight and final specific activity of purified preparations. The purified factor catalyzes the hydrolysis of GTP present in 40 S initiation complexes in the absence of 60 S ribosomal subunits. The presence of 60 S ribosomal subunits neither stimulates nor inhibits the hydrolysis of GTP in the absence of Met-tRNA(f) or other components required for 40 S initiation complex formation. It can be calculated that 1 pmol of eIF-5 protein can catalyze the formation of at least 10 pmol of 80 S initiation complex under the conditions of in vitro initiation reactions.

Original languageEnglish (US)
Pages (from-to)2132-2139
Number of pages8
JournalJournal of Biological Chemistry
Volume260
Issue number4
StatePublished - 1985

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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