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© The Rockefeller University Press, 0021-9525/1999//295 $5.00
The Journal of Cell Biology, Volume 147, Number 2, , 1999 295-306

Original Article

Human Cyclin a Is Required for Mitosis until Mid Prophase



Nobuaki Furunoa, Nicole den Elzena, and Jonathon Pinesa

a Wellcome/Cancer Research Campaign Institute and Department of Zoology, University of Cambridge, Cambridge CB2 1QR, United Kingdom
Wellcome/CRC Institute and Department of Zoology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QR, UK.01223 33408901223 334096

j.pines{at}welc.cam.ac.uk

We have used microinjection and time-lapse video microscopy to study the role of cyclin A in mitosis. We have injected purified, active cyclin A/cyclin-dependent kinase 2 (CDK2) into synchronized cells at specific points in the cell cycle and assayed its effect on cell division. We find that cyclin A/CDK2 will drive G2 phase cells into mitosis within 30 min of microinjection, up to 4 h before control cells enter mitosis. Often this premature mitosis is abnormal; the chromosomes do not completely condense and daughter cells fuse. Remarkably, microinjecting cyclin A/CDK2 into S phase cells has no effect on progress through the following G2 phase or mitosis. In complementary experiments we have microinjected the amino terminus of p21Cip1/Waf1/Sdi1 (p21N) into cells to inhibit cyclin A/CDK2 activity. We find that p21N will prevent S phase or G2 phase cells from entering mitosis, and will cause early prophase cells to return to interphase. These results suggest that cyclin A/CDK2 is a rate-limiting component required for entry into mitosis, and for progress through mitosis until late prophase. They also suggest that cyclin A/CDK2 may be the target of the recently described prophase checkpoint.

Key Words: cyclin • CDK • mitosis • p21 • GFP

© 1999 The Rockefeller University Press

1.used in this paper: CDK, cyclin-dependent kinase; Cdc, cell division cycle

Dr. Furuno's present address is Department of Biology, Kyushu University, Japan.


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Related Article


J. Cell Biol. 1999 147: 1-2. [Full Text] [PDF]





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