INVITRO EFFECTS ON MICROTUBULE DYNAMICS OF PURIFIED XENOPUS M-PHASE-ACTIVATED MAP KINASE

THE protein kinase MAP kinase, also called MAP2 kinase, is a serine/threonine kinase whose activation and phosphorylation are induced by a variety of mitogens 1-6, and which is thought to have a critical role in a network of protein kinases in mitogenic signal transduction 1-7. A burst in kinase activation 8,9 and protein phosphorylation 10 may also be important in triggering the dramatic reorganization of the cell during the transition from interphase to mitosis. The interphase-metaphase transition of microtubule arrays is under the control of p34cd2 kinase 11, a central control element in the G2-M transition of the cell cycle 12. Here we show that a Xenopus kinase, closely related to the mitogen-activated mammalian MAP kinase, is phosphorylated and activated during M phase of meiotic and mitotic cell cycles, and that the interphase-metaphase transition of microtubule arrays can be induced by the addition of purified Xenous M phase-activated MAP kinase or mammalian mitogen-activated MAP kinase to interphase extracts in vitro.