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Published 20 August 2001. doi:10.1083/jcb.200104130
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© The Rockefeller University Press, 0021-9525/2001/8/707 $5.00
The Journal of Cell Biology, Volume 154, Number 4, August 20, 2001 707-718

Article

 Elevating the level of Cdc34/Ubc3 ubiquitin-conjugating enzyme in mitosis inhibits association of CENP-E with kinetochores and blocks the metaphase alignment of chromosomes

Leana M. Topper1, Holger Bastians2, Joan V. Ruderman3 and Gary J. Gorbsky4

1 Department of Cell Biology, University of Virginia, Charlottesville, VA 22908
2 Institute for Molecular Biology and Tumor Research, Philipps University, 35033 Marburg, Germany
3 Department of Cell Biology, Harvard Medical School, Boston, MA 02115
4 Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104

Address correspondence to G.J. Gorbsky, Biomedical Research Center, 975 N.E. 10th St., Rm. 266, Oklahoma City, OK 73104. Tel.: (405) 271-3486. Fax: (405) 271-7158. E-mail: gjg{at}ouhsc.edu

Cdc34/Ubc3 is a ubiquitin-conjugating enzyme that functions in targeting proteins for proteasome-mediated degradation at the G1 to S cell cycle transition. Elevation of Cdc34 protein levels by microinjection of bacterially expressed Cdc34 into mammalian cells at prophase inhibited chromosome congression to the metaphase plate with many chromosomes remaining near the spindle poles. Chromosome condensation and nuclear envelope breakdown occurred normally, and chromosomes showed oscillatory movements along mitotic spindle microtubules. Most injected cells arrested in a prometaphase-like state. Kinetochores, even those of chromosomes that failed to congress, possessed the normal trilaminar plate ultrastructure. The elevation of Cdc34 protein levels in early mitosis selectively blocked centromere protein E (CENP-E), a mitotic kinesin, from associating with kinetochores. Other proteins, including two CENP-E–associated proteins, BubR1 and phospho-p42/p44 mitogen-activated protein kinase, and mitotic centromere-associated kinesin, cytoplasmic dynein, Cdc20, and Mad2, all exhibited normal localization to kinetochores. Proteasome inhibitors did not affect the prometaphase arrest induced by Cdc34 injection. These studies suggest that CENP-E targeting to kinetochores is regulated by ubiquitylation not involving proteasome-mediated degradation.

Key Words: centromere; cell cycle; kinesin; microtubules; proteasome


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