Cyclin A-Cys41 does not undergo cell cycle-dependent degradation in Xenopus extracts.

Truncated cyclin A and cyclin B lacking the N-terminal domain comprising the 'destruction box' escape from proteolysis and arrest cells at metaphase. Mutation of a conserved arginine residue of the destruction domain makes cyclin B resistant to proteolysis. Here we show that mutation of the same residue also makes cyclin A resistant to proteolysis, in either of two situations in which the cyclin degradation pathway is turned on: (i) in Xenopus extracts of activated eggs where the degradation pathway has been permanently turned on by adding a recombinant undegradable cyclin B in which the arginine residue of the destruction box has been substituted by alanine; (ii) in extracts of metaphase II-arrested oocytes after Ca(2+)-dependent inactivation of the cytostatic factor (CSF).