Cell cycle-dependent binding of HMGN proteins to chromatin.
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.
Cherukuri
Srujana
S
Laboratory of Metabolism, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
Hock
Robert
R
Ueda
Tetsuya
T
Catez
Frédéric
F
Rochman
Mark
M
Bustin
Michael
M
D000818:Animals; D002453:Cell Cycle; D002470:Cell Survival; D002843:Chromatin / Q000378:metabolism*; D002877:Chromosomes, Human / Q000378:metabolism; D005453:Fluorescence; D005816:Genetic Complementation Test; D024241:HMGN1 Protein / Q000737:chemistry / Q000378:metabolism*; D024242:HMGN2 Protein / Q000737:chemistry / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D007399:Interphase; D051379:Mice; D008938:Mitosis; D008954:Models, Biological; D010766:Phosphorylation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D051381:Rats
D002843:Chromatin; D024241:HMGN1 Protein; D024242:HMGN2 Protein