Purified cyclin B-cdc2 kinase has been shown previously to trigger cyclin degradation in interphase frog extracts by initiating a cascade of reactions that includes cyclin ubiquitinylation and ends with proteolysis. However, cyclin A-cdc2 kinase was not assayed in these early experiments. Here we have shown that full-length recombinant human cyclin A failed to induce cyclin degradation when it was added to frog extracts free of cyclin B, although it formed an active kinase complex with Xenopus cdc2. A highly purified kinase complex containing a truncated human cyclin A and starfish cdc2 also failed to switch on the cyclin degradation pathway. In contrast, both recombinant cyclin B and highly purified cyclin B-cdc2 kinase readily triggered degradation of both cyclins B and A in frog extracts. Whilst free cyclin A had no inhibitory effect, cyclin A-cdc2 kinase delayed degradation of both cyclins A and B induced by cyclin B-cdc2 kinase. The finding that cyclin A-cdc2 kinase cannot turn on, and even delays, cyclin destruction may be essential to prevent premature inactivation of MPF (maturation-promoting factor) before complete condensation of chromosomes and formation of the metaphase spindle.
Cyclin A-cdc2 kinase does not trigger but delays cyclin degradation in interphase extracts of amphibian eggs
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T. Lorca, J.C. Labbe, A. Devault, D. Fesquet, U. Strausfeld, J. Nilsson, P.A. Nygren, M. Uhlen, J.C. Cavadore, M. Doree; Cyclin A-cdc2 kinase does not trigger but delays cyclin degradation in interphase extracts of amphibian eggs. J Cell Sci 1 May 1992; 102 (1): 55–62. doi: https://doi.org/10.1242/jcs.102.1.55
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