The exchange rate of cyclin A and cyclin B between endogenous p34cdc2 and bacterially expressed GST-cdc2 was measured in concentrated Xenopus egg extracts. The half-lives of the cyclin A.p34cdc2 and the cyclin B.p34cdc2 complexes are estimated as 4 and 15 h, respectively. There is no significant difference in these affinities when they are measured in mitosis, interphase, or during transition between these two states. The tight association between cyclin and p34cdc2 in the cell cycle may be significant for mechanisms of cyclin destruction.
