ISOLATION OF PROTEIN PHOSPHOKINASE FROM THE COMPLEX FORM OF RAT-LIVERDNA POLYMERASE-ALPHA

Protein phosphokinase was found in the complex forms of rat liver DNA polymerase alpha, which also contain 3'-->5' exonuclease, primase, hel icase, and DNA ligase. A 200-kDa protein phosphokinase was obtained fr om the high-molecular-weight DNA polymerase alpha (1000-1500 kDa) isol ated from the nuclear membrane of regenerating liver. In intact liver cells, maximal protein phosphokinase activity was observed in the comp lex form of DNA polymerase alpha isolated from the cytosol, whereas in dividing cells (40 h after partial hepatectomy) it was revealed in th e nuclear membrane. Protein phosphokinase activity increases sevenfold as the cells progress from the G(o) to S phase of the cell cycle. The major properties of protein phosphokinase are characterized.