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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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A minor fraction of HMG1 cofractionates with polynucleosomes in sucrose gradients. Nuclei of NIH 3T3 fibroblasts  were partially digested with micrococcal nuclease, lysed, and sedimented through a sucrose gradient (see Materials and Methods).  Individual fractions were analyzed by Western blotting for the  presence of HMG1 and histone H1; DNA was also extracted  from the fractions and analyzed on a 2% agarose gel.
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Figure 6: A minor fraction of HMG1 cofractionates with polynucleosomes in sucrose gradients. Nuclei of NIH 3T3 fibroblasts were partially digested with micrococcal nuclease, lysed, and sedimented through a sucrose gradient (see Materials and Methods). Individual fractions were analyzed by Western blotting for the presence of HMG1 and histone H1; DNA was also extracted from the fractions and analyzed on a 2% agarose gel.

Mentions: The results shown above suggest that the bulk of HMG1 is not associated with mitotic chromatin. To examine HMG1's association to chromatin during interphase, nuclei of NIH 3T3 fibroblasts were partially digested with micrococcal nuclease, and nucleosomal particles were fractionated on sucrose gradients (Fig. 6). Consistent with previous data, histone H1 was found associated with mono- and polynucleosomes. Most of HMG1, however, was recovered at the top of the gradient in fractions that do not contain DNA; only longer exposures of the Western blot revealed a minor amount of HMG1 in the fractions containing polynucleosomes (Fig. 6, lanes 20–26).


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)

A minor fraction of HMG1 cofractionates with polynucleosomes in sucrose gradients. Nuclei of NIH 3T3 fibroblasts  were partially digested with micrococcal nuclease, lysed, and sedimented through a sucrose gradient (see Materials and Methods).  Individual fractions were analyzed by Western blotting for the  presence of HMG1 and histone H1; DNA was also extracted  from the fractions and analyzed on a 2% agarose gel.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 6: A minor fraction of HMG1 cofractionates with polynucleosomes in sucrose gradients. Nuclei of NIH 3T3 fibroblasts were partially digested with micrococcal nuclease, lysed, and sedimented through a sucrose gradient (see Materials and Methods). Individual fractions were analyzed by Western blotting for the presence of HMG1 and histone H1; DNA was also extracted from the fractions and analyzed on a 2% agarose gel.
Mentions: The results shown above suggest that the bulk of HMG1 is not associated with mitotic chromatin. To examine HMG1's association to chromatin during interphase, nuclei of NIH 3T3 fibroblasts were partially digested with micrococcal nuclease, and nucleosomal particles were fractionated on sucrose gradients (Fig. 6). Consistent with previous data, histone H1 was found associated with mono- and polynucleosomes. Most of HMG1, however, was recovered at the top of the gradient in fractions that do not contain DNA; only longer exposures of the Western blot revealed a minor amount of HMG1 in the fractions containing polynucleosomes (Fig. 6, lanes 20–26).

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