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Vol. 19, Issue 5, 1816-1824, May 2008

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Cell Cycle-dependent Binding of HMGN Proteins to Chromatin

Srujana Cherukuri^*, Robert Hock, Tetsuya Ueda^*, Frédéric Catez^*,, Mark Rochman^*, and Michael Bustin^*

*Laboratory of Metabolism, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892; Department of Cell and Developmental Biology, University of Wuerzburg, 97074 Wuerzburg, Germany; Université Lyon 1, Lyon, F-69003, France and Centre National de la Recherche Scientifique, Unité Mixte de Recherche 5534, Centre de Génétique Moléculaire et Cellulaire, Villeurbanne, F-69622, France

Submitted October 9, 2007; Revised February 6, 2008; Accepted February 8, 2008
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, whereas 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 proteins associate with chromatin with low affinity as monomers, and they do not form specific complexes. Our studies demonstrate that the mode of binding of HMGNs to chromatin is cell cycle dependent.

Address correspondence to: Michael Bustin (bustin{at}helix.nih.gov)