Further characterization of eukaryotic initiation factor 5 from rabbit reticulocytes. Immunochemical characterization and phosphorylation by casein kinase II

J Biol Chem. 1989 Mar 25;264(9):5134-40.

Abstract

Eukaryotic initiation factor (eIF)-5, isolated from rabbit reticulocyte lysates, is a monomeric protein of Mr = 58,000-62,000. Immunochemical methods were employed to identify eIF-5 in crude cell lysates. Antisera against purified denatured eIF-5 were prepared in rabbits and characterized by immunoblotting and immunoprecipitation techniques using native and denatured eIF-5 as antigens. Monospecific antibodies to denatured eIF-5 were affinity-purified using eIF-5 blotted onto aminophenylthioether paper. Rabbit reticulocytes, HeLa cells and mouse L cells were lysed directly into a denaturing buffer containing 3% sodium dodecyl sulfate. The denatured proteins were analyzed by polyacrylamide gel electrophoresis followed by immunoblotting with anti-eIF-5 antibodies. With each lysate, one major immunoreactive polypeptide was observed whose molecular weight corresponded to that of purified eIF-5 (Mr = 58,000-62,000). No degradation products or precursor forms of molecular weight higher than 62,000 were detected in any lysate. These results indicate that isolated eIF-5 is the same size as that found in crude lysates. Additional characterization of eIF-5 indicates that purified eIF-5 can be phosphorylated at serine residues in vitro by casein kinase II. Furthermore, in vitro phosphorylated eIF-5 retains full biological activity in catalyzing the joining of 60 S ribosomal subunits to a preformed 40 S ribosomal initiation complex to form an 80 S initiation complex. Based on its specific activity, we demonstrate that 1 pmol of rabbit reticulocyte eIF-5 mediates the formation of approximately 180 pmol of 80 S initiation complex under the conditions of in vitro initiation reactions.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Antibody Specificity
  • Casein Kinases
  • Cell Fractionation
  • Eukaryotic Initiation Factor-5
  • Immune Sera
  • Immunoblotting / methods
  • Molecular Weight
  • Peptide Initiation Factors / immunology
  • Peptide Initiation Factors / isolation & purification*
  • Peptide Initiation Factors / physiology
  • Phosphorylation
  • Protein Kinases*
  • Rabbits
  • Reticulocytes / analysis*

Substances

  • Eukaryotic Initiation Factor-5
  • Immune Sera
  • Peptide Initiation Factors
  • Protein Kinases
  • Casein Kinases