title: Phosphorylation in vitro of eukaryotic initiation factors IF-E2 and IF-E3 by protein kinases.
abstract: Purified protein synthesis initiation factors IF-E2 and IF-E3 from rabbit reticulocytes were phosphorylated in vitro with protein kinases isolated from the same source. The highest levels of phosphorylation resulted from incubation of the factors with a cyclic nucleotide-independent protein kinase previously shown to have specificity for acidic proteins. The extent of phosphorylation of initiation factor IF-E2 was between 0.3 and 0.4 mol of phosphate per mol of factor complex, with either ATP or GTP as phosphoryl donor. Initiation factor IF-E2 is composed of three nonidentical polypeptides; only the polypeptide with a molecular weight of 52,000 was phosphorylated. The extent of phosphorylation of initiation factor IF-E3 was between 0.7 and 1.0 mol of phosphate per mol of factor complex with GTP as phosphoryl donor; with ATP, less phosphorylation of the factor was obtained. Initiation factor IF-E3 is composed of 9 to 11 nonidentical polypeptides; only 2 of these, with molecular weights of 120,000 and 70,000, were phosphorylated. A lower level of phosphorylation of initiation factor IF-E3 was found with the cyclic AMP-dependent protein kinase; the polypeptide of molecular weight 140,000 was the major site of phosphorylation.
mesh_terms: D000255:Adenosine Triphosphate; D000818:Animals; D004591:Electrophoresis, Polyacrylamide Gel; D006160:Guanosine Triphosphate; D008970:Molecular Weight; D010448:Peptide Initiation Factors; D006656:Protamine Kinase / Q000378:metabolism; D011494:Protein Kinases / Q000097:blood / Q000378:metabolism*; D011817:Rabbits; D012156:Reticulocytes / Q000378:metabolism
chemical_list: D010448:Peptide Initiation Factors; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D011494:Protein Kinases; D006656:Protamine Kinase