We have previously shown that the Dictyostelium discoideum ribosomal protein L19 specifically binds Ca2+/calmodulin [Sonneman et al. (1991) J. Biol. Chem. 266, 23091-23096]. To investigate the role of calmodulin in the regulation of protein synthesis, we have now established an in vitro protein synthesizing system from Dictyostelium cells which can elongate polypeptide chains with high efficiency. Various calmodulin antagonists affected translation in this system. The inhibitory effects of the antagonists could be partially reversed by addition of calmodulin. A monoclonal antibody against D. discoideum calmodulin also specifically inhibited protein synthesis. Similar effects of calmodulin antagonists were found in a standard wheat germ in vitro translation system.
