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A more recent version of this article appeared on May 1, 2008
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Submitted on October 9, 2007
Revised on February 6, 2008
Accepted on February 8, 2008
*Laboratory of Metabolism, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892;
Department of Cell and Developmental Biology, University of Wuerzburg, Germany and Université Lyon 1, Lyon, F-69003, France;
CNRS, UMR5534, Centre de génétique moléculaire et cellulaire, Villeurbanne, F-69622, France
Monitoring Editor: Wendy Bickmore
Throughout the cell cycle the histones remain associated with DNA but the repertoire of proteins associated with the chromatin fiber continuously changes. The chromatin interaction of HMGNs, a family of nucleosome binding proteins that modulates the structure and activity of chromatin, during the cell cycle is controversial. Immunofluorescence studies demonstrated that HMGNs are not associated with chromatin while live cell imaging indicated that they are present in mitotic chromosomes.
To resolve this controversy we examined the organization of wild type and mutated HMGN1 and HMGN2 proteins in the cell nucleus by using immunofluorescence studies, live cell imaging, gel mobility shift assays and bimolecular fluorescence complementation (BiFC). We find that during interphase HMGNs bind specifically to nucleosomes and form homodimeric complexes that yield distinct BiFC signals. In metaphase, the nucleosomal binding domain of the protein is inactivated and the protein associate with chromatin with low affinity as monomers, and do not form specific complexes. Our studies demonstrate that the mode of binding of HMGN to chromatin is cell cycle dependent.