32P-labeled ornithine decarboxylase was isolated by immunoprecipitation from murine erythroleukemia cells incubated in a medium containing [32P]ortophosphoric acid. Analysis of immunoprecipitate by SDS-polyacrylamide gel electrophoresis and autoradiography revealed a radiolabeled band, which corresponded to the position of mouse ornithine decarboxylase, phosphorylated in vitro by casein kinase-2. A preparation of casein kinase-2 purified from nuclei of erythroleukemia cells could also phosphorylate mouse ornithine decarboxylase.
