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High mobility group 1 protein is not stably associated with the chromosomes of somatic cells.

Falciola L, Spada F, Calogero S, Langst G, Voit R, Grummt I, Bianchi ME - J. Cell Biol. (1997)

Bottom Line: The protein is excluded from nucleoli and is not associated to specific nuclear structures but rather appears to be uniformly distributed.HMG1 can bind in vitro to reconstituted core nucleosomes but is not stably associated to chromatin in live cells.During interphase, HMG1 readily diffuses out of nuclei after permeabilization of the nuclear membranes with detergents, whereas histone H1 remains associated to chromatin.

View Article: PubMed Central - PubMed

Affiliation: Dipartimento di Genetica e di Biologia dei Microrganismi, Universitá di Milano, Italy.

ABSTRACT
High mobility group 1 (HMG1) protein is an abundant and conserved component of vertebrate nuclei and has been proposed to play a structural role in chromatin organization, possibly similar to that of histone H1. However, a high abundance of HMG1 had also been reported in the cytoplasm and on the surface of mammalian cells. We conclusively show that HMG1 is a nuclear protein, since several different anti-HMG1 antibodies stain the nucleoplasm of cultured cells, and epitope-tagged HMG1 is localized in the nucleus only. The protein is excluded from nucleoli and is not associated to specific nuclear structures but rather appears to be uniformly distributed. HMG1 can bind in vitro to reconstituted core nucleosomes but is not stably associated to chromatin in live cells. At metaphase, HMG1 is detached from condensed chromosomes, contrary to histone H1. During interphase, HMG1 readily diffuses out of nuclei after permeabilization of the nuclear membranes with detergents, whereas histone H1 remains associated to chromatin. These properties exclude a shared function for HMG1 and H1 in differentiated cells, in spite of their similar biochemical properties. HMG1 may be stably associated only to a very minor population of nucleosomes or may interact transiently with nucleosomes during dynamic processes of chromatin remodeling.

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HMG1 binds to reconstituted mononucleosomes. A labeled DNA fragment (176 bp) was assembled into mononucleosomes, incubated with increasing amounts (0, 10, 50, 100, and 500  ng) of HMG1 (lanes 6–10), and electrophoresed on a 0.7% agarose gel. DNA not assembled in nucleosomes was treated similarly for comparison (lanes 1–5). The bands corresponding to free  DNA, to nucleosome particles, and to HMG1–nucleosome complexes are indicated.
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Figure 3: HMG1 binds to reconstituted mononucleosomes. A labeled DNA fragment (176 bp) was assembled into mononucleosomes, incubated with increasing amounts (0, 10, 50, 100, and 500 ng) of HMG1 (lanes 6–10), and electrophoresed on a 0.7% agarose gel. DNA not assembled in nucleosomes was treated similarly for comparison (lanes 1–5). The bands corresponding to free DNA, to nucleosome particles, and to HMG1–nucleosome complexes are indicated.

Mentions: Nightingale et al. (1996) have recently shown that Xenopus HMG1 forms stable complexes with in vitro reconstituted nucleosomes, similar to the complexes formed by histone H1 and its embryonic variant B4. Both HMG1 and B4 associate with linker DNA and protect it from micrococcal nuclease digestion. We confirmed these observations with mammalian HMG1: HMG1 binds very weakly to linear DNA not organized in nucleosomes, whereas it forms complexes with in vitro reconstituted core mononucleosomes (Fig. 3). Nucleosomes lacking linker DNA were unable to bind HMG1 (results not shown).


High mobility group 1 protein is not stably associated with the chromosomes of somatic cells.

Falciola L, Spada F, Calogero S, Langst G, Voit R, Grummt I, Bianchi ME - J. Cell Biol. (1997)

HMG1 binds to reconstituted mononucleosomes. A labeled DNA fragment (176 bp) was assembled into mononucleosomes, incubated with increasing amounts (0, 10, 50, 100, and 500  ng) of HMG1 (lanes 6–10), and electrophoresed on a 0.7% agarose gel. DNA not assembled in nucleosomes was treated similarly for comparison (lanes 1–5). The bands corresponding to free  DNA, to nucleosome particles, and to HMG1–nucleosome complexes are indicated.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2139855&req=5

Figure 3: HMG1 binds to reconstituted mononucleosomes. A labeled DNA fragment (176 bp) was assembled into mononucleosomes, incubated with increasing amounts (0, 10, 50, 100, and 500 ng) of HMG1 (lanes 6–10), and electrophoresed on a 0.7% agarose gel. DNA not assembled in nucleosomes was treated similarly for comparison (lanes 1–5). The bands corresponding to free DNA, to nucleosome particles, and to HMG1–nucleosome complexes are indicated.
Mentions: Nightingale et al. (1996) have recently shown that Xenopus HMG1 forms stable complexes with in vitro reconstituted nucleosomes, similar to the complexes formed by histone H1 and its embryonic variant B4. Both HMG1 and B4 associate with linker DNA and protect it from micrococcal nuclease digestion. We confirmed these observations with mammalian HMG1: HMG1 binds very weakly to linear DNA not organized in nucleosomes, whereas it forms complexes with in vitro reconstituted core mononucleosomes (Fig. 3). Nucleosomes lacking linker DNA were unable to bind HMG1 (results not shown).

Bottom Line: The protein is excluded from nucleoli and is not associated to specific nuclear structures but rather appears to be uniformly distributed.HMG1 can bind in vitro to reconstituted core nucleosomes but is not stably associated to chromatin in live cells.During interphase, HMG1 readily diffuses out of nuclei after permeabilization of the nuclear membranes with detergents, whereas histone H1 remains associated to chromatin.

View Article: PubMed Central - PubMed

Affiliation: Dipartimento di Genetica e di Biologia dei Microrganismi, Universitá di Milano, Italy.

ABSTRACT
High mobility group 1 (HMG1) protein is an abundant and conserved component of vertebrate nuclei and has been proposed to play a structural role in chromatin organization, possibly similar to that of histone H1. However, a high abundance of HMG1 had also been reported in the cytoplasm and on the surface of mammalian cells. We conclusively show that HMG1 is a nuclear protein, since several different anti-HMG1 antibodies stain the nucleoplasm of cultured cells, and epitope-tagged HMG1 is localized in the nucleus only. The protein is excluded from nucleoli and is not associated to specific nuclear structures but rather appears to be uniformly distributed. HMG1 can bind in vitro to reconstituted core nucleosomes but is not stably associated to chromatin in live cells. At metaphase, HMG1 is detached from condensed chromosomes, contrary to histone H1. During interphase, HMG1 readily diffuses out of nuclei after permeabilization of the nuclear membranes with detergents, whereas histone H1 remains associated to chromatin. These properties exclude a shared function for HMG1 and H1 in differentiated cells, in spite of their similar biochemical properties. HMG1 may be stably associated only to a very minor population of nucleosomes or may interact transiently with nucleosomes during dynamic processes of chromatin remodeling.

Show MeSH
Related in: MedlinePlus