NEWLY SYNTHESIZED PROTEIN(S) MUST ASSOCIATE WITH P34(CDC2) TO ACTIVATE MAP KINASE AND MPF DURING PROGESTERONE-INDUCED MATURATION OF XENOPUS OOCYTES

The meiotic maturation of Xenopus oocytes triggered by progesterone requires new protein synthesis to activate both maturation-promoting factor (MPF) and mitogen-activated protein kinase (MAP kinase). Injection of mRNA encoding mutant p34(cdc2) (K33R) that can bind cyclins but lacks protein kinase activity strongly inhibited progesterone-induced activation of both MPF and MAP kinase in Xenopus oocytes. Similar results were obtained by injection of GST-p34(cdc2) K33R protein or by injection of a monoclonal antibody (A17) against p34(cdc2) that blocks its activation by cyclins. Both the dominant-negative p34(cdc2) and monoclonal antibody A17 blocked the accumulation of p39(mos) and activation of MAP kinase in response to progesterone, as well as blocking the appearance of MPF, although they did not inhibit the translation of p39(mos) mRNA. These results suggest that: (i) activation of free p34(cdc2) by newly made proteins, probably cyclin(s), is normally required for the activation of both MPF and MAP kinase by progesterone in Xenopus oocytes; (ii) the activation of translation of cyclin mRNA normally precedes, and does not require either MPF or MAP kinase activity; and (iii) de novo synthesis and accumulation of p39(mos) is probably both necessary and sufficient for the activation of MAP kinase in response to progesterone.