Cell Volume 114, Issue 1 , 11 July 2003, Pages 87-98
Yinghui Mao (1), Ariane Abrieu (1)(3) and Don W. Cleveland (1)(2)
(1) Ludwig Institute for Cancer Research, 9500 Gilman Drive, La Jolla, CA 92093, USA
(2) Department of Cellular and Molecular Medicine, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA
Received 6 November 2002; accepted 2 June 2003 Published: July 10, 2003; Available online 15 July 2003.
The mitotic checkpoint prevents advance to anaphase prior to successful attachment of every centromere/kinetochore to mitotic spindle microtubules. Using purified components and Xenopus egg extracts, the kinetochore-associated microtubule motor CENP-E is now shown to be the activator of the essential checkpoint kinase BubR1. Since kinase activity and the checkpoint are silenced following CENP-E-dependent microtubule attachment in extracts or binding of CENP-E antibodies that do not disrupt CENP-E association with BubR1, CENP-E mediates silencing of BubR1 signaling. Checkpoint signaling requires the normal level of BubR1 containing a functional Mad3 domain implicated in Cdc20 binding, but only a small fraction need be kinase competent. This supports bifunctional roles for BubR1 in the checkpoint: an enzymatic one requiring CENP-E-dependent activation of its kinase activity at kinetochores and a stoichiometric one as a direct inhibitor of Cdc20.