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Molecular and Cellular Biology, February 1999, p. 1016-1024, Vol. 19, No. 2
Shanghai Research Center of Life Sciences,
Chinese Academy of Sciences, Shanghai 200031, China
Received 12 May 1998/Returned for modification 3 July 1998/Accepted 26 October 1998
Mitosin is a 350-kDa human nuclear protein which transiently
associates with centromeres and spindle poles in M phase.
Ultrastructure studies reveal that it is located at the outer
kinetochore plate. In this work, we explored the detailed structural
basis and dynamics of the mitosin-kinetochore interaction. Two major
regions important for targeting to centromeres were identified by
analyzing different deletion mutants expressed in CHO cells: (i) the
"core region" between amino acids 2792 and 2887, which was
essential for the centromere localization of mitosin; and (ii) the
internal repeats between residues 2094 and 2487, which cooperated with
the core region to achieve strong mitosin-kinetochore interaction. The core region is characteristic of two leucine zipper motifs. Deletion of
either motif abolished the centromere localization activity. In
addition, Cys2864, adjacent to the second motif, was also
essential for the activity of the core region. In contrast, the
internal repeats alone were insufficient for centromere localization.
We propose that this region may serve as a regulatory domain to
facilitate interaction of the core region with the kinetochore. We
showed that mitosin molecules entering nuclei after nuclear envelope
breakdown (NEBD) were not assembled onto kinetochores efficiently,
suggesting that the mitosin-kinetochore interaction is stabilized prior
to NEBD. This result supports the idea of an ordered process for
kinetochore assembly. Our data also suggest that mitosin might interact
with chromatin in interphase. Evidence for coordinated regulation
between the centromere-targeting and the putative chromatin-binding
activities is also provided.
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Structural Requirements and Dynamics of Mitosin-Kinetochore
Interaction in M Phase
*
Mailing address: Shanghai Research Center of Life
Sciences, Chinese Academy of Sciences, 320 Yue Yang Rd., Shanghai
200031, China. Phone: 86-21-64748700, ext. 169. Fax: 86-21-64333084. E-mail: xlzhu{at}iris.shlc.ac.cn.
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