Phosphorylation of elongation factor 1 (EF-1) and valyl-tRNA synthetase by protein kinase C and stimulation of EF-1 activity

• Published in: The Journal of biological chemistry 1991-07, Vol.266 (19), p.12574-12580
• Main Authors: VENEMA, R. C, PETERS, H. I, TRAUGH, J. A
• Format: Article
• Language: English
• Subjects: Amino Acyl-tRNA Synthetases - metabolism; Animals; Autoradiography; Biological and medical sciences; Cell physiology; Chromatography, Gel; Electrophoresis, Gel, Two-Dimensional; Electrophoresis, Polyacrylamide Gel; Fundamental and applied biological sciences. Psychology; Molecular and cellular biology; Peptide Elongation Factor 1; Peptide Elongation Factors - metabolism; Peptide Mapping; Phosphorylation; Protein Kinase C - metabolism; Rabbits; Responses to growth factors, tumor promotors, other factors; Reticulocytes - drug effects; Reticulocytes - enzymology; Tetradecanoylphorbol Acetate - pharmacology; Valine-tRNA Ligase - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)98937-4

A high Mr complex isolated from rabbit reticulocytes contains valyl-tRNA synthetase and the four subunits of elongation factor 1 (EF-1). Previously, valyl-tRNA synthetase and the alpha, beta, and delta subunits of EF-1 were shown to be phosphorylated in reticulocytes in response to phorbol 12-myristate 13-acetate (PMA). Phosphorylation of the complex was accompanied by an increase in both valyl-tRNA synthetase and EF-1 activity (Venema, R. C., Peters, H. I., and Traugh, J. A. (1991) J. Biol. Chem., 266, 11993-11998). To investigate phosphorylation of the valyl-tRNA synthetase EF-1 complex in vitro by protein kinase C, the complex has been purified to apparent homogeneity from rabbit reticulocytes by gel filtration on Bio-Gel A-5m, affinity chromatography on tRNA-Sepharose, and fast protein liquid chromatography on Mono Q. Valyl-tRNA synthetase and the beta and delta subunits of EF-1 in the complex are highly phosphorylated by protein kinase C (0.5-0.9 mol of phosphate/mol of subunit), while EF-1 alpha is phosphorylated to a lesser extent (0.2 mol/mol). However, the isolated EF-1 alpha subunit is highly phosphorylated (2.0 mol/mol). Phosphopeptide mapping of EF-1 alpha shows that the same sites are modified by protein kinase C in vitro and in PMA-treated cells. Phosphorylation of the valyl-tRNA synthetase.EF-1 complex results in a 3-fold increase in activity of EF-1 as measured by poly(U)-directed polyphenylalanine synthesis; no effect of phosphorylation is detected with valyl-tRNA synthetase and isolated EF-1 alpha. Thus, phosphorylation and activation of EF-1 by protein kinase C, which has been shown to occur in vitro as well as in reticulocytes, may have a role in PMA stimulation of translational rates.