Mitotic arrest caused by the amino terminus of Xenopus cyclin B2.
Progression through mitosis requires the inactivation of the protein kinase activity of the p34cdc2-cyclin complex by a mechanism involving the degradation of cyclin. We have examined the stability in Xenopus egg extracts of radiolabeled Xenopus or sea urchin B-type cyclins synthesized in reticulocyte lysates. Xenopus cyclin B2 and sea urchin cyclin B were stable in metaphase extracts from unfertilized eggs but were specifically degraded following addition of Ca2+ to the extracts. The degradation of either cyclin was inhibited by the addition of an excess of unlabeled Xenopus cyclin B2 but not by the addition of a number of control proteins. A truncated protein containing only the amino terminus of Xenopus cyclin B2, including sequences known to be essential for cyclin degradation in other species, also inhibited cyclin degradation, even though the truncated protein was stable in extracts following Ca2+ addition. The addition of the truncated protein did not stimulate histone H1 kinase activity in extracts but prevented the loss of H1 kinase activity that normally follows Ca2+ addition to metaphase extracts. When the amino-terminal fragment was added to extracts capable of several cell cycles in vitro, progression through the first mitosis was inhibited and elevated histone H1 kinase activity was maintained. These results indicate that although the amino terminus of cyclin does not contain all of the information necessary for cyclin destruction, it is capable of interacting with components of the cyclin destruction pathway and thereby preventing the degradation of full-length cyclins.
Department of Cellular & Structural Biology, University of Colorado School of Medicine, Denver 80262.
H M
HM
van der Velden
M J
MJ
Lohka
D000818:Animals; D002474:Cell-Free System; D016213:Cyclins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D004926:Escherichia coli / Q000235:genetics; D008677:Metaphase / Q000187:drug effects; D008938:Mitosis / Q000187:drug effects*; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D006656:Protamine Kinase / Q000378:metabolism; D011480:Protease Inhibitors / Q000494:pharmacology; D011993:Recombinant Fusion Proteins / Q000378:metabolism / Q000494:pharmacology; D012617:Sea Urchins; D013329:Structure-Activity Relationship; D014982:Xenopus laevis
D016213:Cyclins; D010446:Peptide Fragments; D011480:Protease Inhibitors; D011993:Recombinant Fusion Proteins; D006656:Protamine Kinase