Activation of Xenopus eggs by the kinase inhibitor 6-DMAP suggests a differential regulation of cyclin B and p39(mos) proteolysis

In Xenopus eggs, metaphase II arrest is due to the cytostatic factor that m aintains a high level of MPF activity. Kinases are important in this phenom enon since p39(mos) and MAPK play a part in the cytostatic activity whereas p34(cdc2) iS the catalytic subunit of MPF, Fertilization induces a rise in intracellular calcium leading to egg activation that can be mimicked by ca lcium-increasing agents such as calcium ionophore. We have performed on Xen opus eggs a biochemical comparison of the effects of the kinase inhibitor 6 -DMAP and the calcium ionophore. Both drugs were able to induce pronucleus formation but the underlying molecular events were different. The inactivat ion of MAPK occurred earlier in eggs exposed to 6-DMAP. Cyclins B1 and B2 w ere stable and p39(mos) was proteolysed in 6-DMAP-treated eggs while the th ree proteins underwent degradation in A23187-treated ones. These results su ggest a differential regulation of ubiquitin-dependent proteolysis of cycli n B and p39(mos). (C) 1999 Academic Press.