A post-ribosomal supernatant from activated Xenopus eggs that displays post-translationally regulated oscillation of its cdc2+ mitotic kinase activity.

A cell-free extract prepared from activated Xenopus eggs by high-speed centrifugation displays one spontaneous cycle of activation and inactivation of histone H1 kinase and MPF activity that is largely attributable to Xenopus p32cdc2. The timing of the oscillation closely follows that observed in intact eggs, is associated with large changes in endogenous protein phosphorylation and depends entirely on post-translational events. The extract can be fractionated into soluble and particulate material, both of which components are required for the oscillatory behaviour. Kinase activation does not require Mg+ ATP, but its rapid inactivation, which coincides with the destruction of cyclin, is inhibited both by EDTA and the protein kinase inhibitor 6-dimethylaminopurine. This suggests that protein phosphorylation is required for cyclin destruction and kinase inactivation.