CYTOSOLIC NUCLEOSIDE DIPHOSPHATE KINASE ASSOCIATED WITH THE TRANSLATION APPARATUS MAY PROVIDE GTP FOR PROTEIN-SYNTHESIS

Elongation of nascent polypeptides in a Dictyostelium discoideum in vi tro translation system did not require the addition of ATP and GTP whe n creatine phosphate and creatine phosphokinase were present. However, depletion of the exogenous energy supply completely abolished incorpo ration of amino acids. Addition of dTTP, a nucleoside triphosphate tha t can be utilized by nucleoside diphosphate kinase (NDP kinase) to pho sphorylate endogenous ADP and GDP, partially restored protein synthesi s. Dictyostelium ribosomes were found to contain NDP kinase activity t hat could not be released by 1 M KCl. Thermal denaturation studies, sp ecific inhibition with antibodies, and Western blotting identify the a ctivity as cytosolic NDP kinase. These data support the idea that GTP can be fed into the translation machinery efficiently by NDP kinase as sociated with active ribosomes. (C) 1995 Academic Press. Inc.