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Dynamics of inner kinetochore assembly and maintenance in living cells
Correspondence to P. Hemmerich: phemmer{at}fli-leibniz.de; or S. Diekmann: diekmann{at}fli-leibniz.de
To investigate the dynamics of centromere organization, we have assessed the exchange rates of inner centromere proteins (CENPs) by quantitative microscopy throughout the cell cycle in human cells. CENP-A and CENP-I are stable centromere components that are incorporated into centromeres via a "loading-only" mechanism in G1 and S phase, respectively. A subfraction of CENP-H also stays stably bound to centromeres. In contrast, CENP-B, CENP-C, and some CENP-H and hMis12 exhibit distinct and cell cycle–specific centromere binding stabilities, with residence times ranging from seconds to hours. CENP-C and CENP-H are immobilized at centromeres specifically during replication. In mitosis, all inner CENPs become completely immobilized. CENPs are highly mobile throughout bulk chromatin, which is consistent with a binding-diffusion behavior as the mechanism to scan for vacant high-affinity binding sites at centromeres. Our data reveal a wide range of cell cycle–specific assembly plasticity of the centromere that provides both stability through sustained binding of some components and flexibility through dynamic exchange of other components.
S. Weidtkamp-Peters' present address is Institut für Physikalische Chemie II, Heinrich-Heine-Universität, 40225 Düsseldorf, Germany.
L. Schmiedeberg's present address is Wellcome Trust Centre for Cell Biology, University of Edinburgh, Edinburgh EH9 3JR, Scotland.
Abbreviations used in this paper: CENP, centromere protein; FCS, fluorescence correlation spectroscopy; mRFP, monomeric red fluorescent protein; PCNA, proliferating cell nuclear antigen.
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