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Molecular and Cellular Biology, September 2000, p. 6996-7006, Vol. 20, No. 18
Department of Biological Chemistry, College
of Medicine, University of California, Irvine, California
92697-1700,1 and Howard Hughes
Medical Institute, Department of Molecular and Cell Biology,
University of California, Berkeley, California
94720-32022
Received 11 January 2000/Returned for modification 9 February
2000/Accepted 15 June 2000
Structural maintenance of chromosomes (SMC) family proteins play
critical roles in structural changes of chromosomes. Previously, we
identified two human SMC family proteins, hCAP-C and hCAP-E, which form
a heterodimeric complex (hCAP-C-hCAP-E) in the cell. Based on the
sequence conservation and mitotic chromosome localization, hCAP-C-hCAP-E was determined to be the human ortholog of the
Xenopus SMC complex, XCAP-C-XCAP-E. XCAP-C-XCAP-E is a
component of the multiprotein complex termed condensin, required for
mitotic chromosome condensation in vitro. However, presence of such a
complex has not been demonstrated in mammalian cells.
Coimmunoprecipitation of the endogenous hCAP-C-hCAP-E complex from
HeLa extracts identified a 155-kDa protein interacting with
hCAP-C-hCAP-E, termed condensation-related SMC-associated protein 1 (CNAP1). CNAP1 associates with mitotic chromosomes and is homologous to
Xenopus condensin component XCAP-D2, indicating the
presence of a condensin complex in human cells. Chromosome association
of human condensin is mitosis specific, and the majority of condensin
dissociates from chromosomes and is sequestered in the cytoplasm
throughout interphase. However, a subpopulation of the complex was
found to remain on chromosomes as foci in the interphase nucleus.
During late G2/early prophase, the larger nuclear condensin
foci colocalize with phosphorylated histone H3 clusters on partially
condensed regions of chromosomes. These results suggest that
mitosis-specific function of human condensin may be regulated by cell
cycle-specific subcellular localization of the complex, and the nuclear
condensin that associates with interphase chromosomes is involved in
the reinitiation of mitotic chromosome condensation in conjunction with
phosphorylation of histone H3.
0270-7306/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
A Human Condensin Complex Containing hCAP-C-hCAP-E
and CNAP1, a Homolog of Xenopus XCAP-D2, Colocalizes with
Phosphorylated Histone H3 during the Early Stage of Mitotic
Chromosome Condensation
*
Corresponding author. Mailing address: 240D Med Sci I,
Department of Biological Chemistry, College of Medicine, University of
California, Irvine, CA 92697-1700. Phone: (949) 824-8215. Fax: (949)
824-2688. E-mail: kyokomor{at}uci.edu.
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