DIRECT ACTIVATION OF P34CDC2-PROTEIN KINASE WITHOUT PRECEDING PHOSPHORYLATION DURING MEIOTIC CELL-CYCLE IN MOUSE OOCYTES

During the late phase of the first and the second meiotic cell cycles, the phosphorylated form of p34cdc2 was not detected and sodium orthovanadate, an inhibitor of tyrosine phosphatase, did not inhibit the activation of histone H1 kinase, whereas it inhibited the activation of the kinase and dephosphorylation of p34cdc2 during the early phase of the first meiosis and mitotic cell cycle. These results indicate that the phosphorylation of p34cdc2 is not a prerequisite for its activation. The significance of the absence of phosphorylation in meiotic cell cycle is discussed.