Evidence for a shared structural role for HMG1 and linker histones B4 and H1 in organizing chromatin.

Nightingale, Karl P.; Dimitrov, Stéfan; Reeves, Raymond; Wolffe, Alan P.

doi:10.1002/j.1460-2075.1996.tb00387.x

Cited by 156 publications

(132 citation statements)

References 101 publications

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“…3C). This result is at variance with the result obtained with the X. borealis 5 S rDNA (10,11); the latter result may be due to the artifacts connected to the use of the 5 S gene sequence for MNase-based assays of protein protection. We have been able to observe the cleavages corresponding to 5/15 bp protection reported previously (10,11) upon digestion of free DNA or core particles (12).…”

Section: Hmg1 Protection Of Linker Dna 26290contrasting

confidence: 76%

“…The choice between two alternative binding sites is probably dictated by DNA sequences in the linker region (8). The location of HMG1, on the other hand, has been so far studied on reconstitutes on only one DNA sequence, the 5 S rDNA from Xenopus borealis (10,11). In this specific case, it was reported that HMG1 interacts with linker DNA in the same way as does histone H1, protecting ϳ5 bp 1 on one side of the nucleosome core and ϳ15 bp on the other side (10,11).…”

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confidence: 99%

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The Non-histone Chromatin Protein HMG1 Protects Linker DNA on the Side Opposite to That Protected by Linker Histones

Holde

Zlatanova

1998

Journal of Biological Chemistry

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Linker histones and HMG1/2 constitute the two major proteins that bind to linker DNA in chromatin. While the location of linker histones on the nucleosome has attracted considerable research effort, only a few studies have addressed the location of HMG1 in the particles. In this study, we use a procedure based on micrococcal nuclease digestion of reconstituted nucleosomal particles to which HMG1 has been bound, followed by analysis of the protected DNA by restriction nuclease digestion, to locate the HMG1 binding site. Nucleosomal particles were reconstituted on a 235-base pair DNA fragment, which is known to be a strong nucleosome positioning sequence. The results unequivocally show that HMG1 protects linker DNA on one side of the core particle. Importantly, and possibly of physiological relevance, the linker DNA site protected by HMG1 was located on the side opposite to that already shown to be protected by linker histone binding.Linker histones (H1, H5, and its cognates) and the nonhistone chromatin proteins HMG1 and HMG2 are the major proteins that bind to linker DNA between successive nucleosomes in the chromatin fiber (for recent reviews, See Refs. 1-4). The two proteins are believed to play roles in transcription regulation, the conventional view being that linker histones are general repressors of transcription, whereas HMG1/2 are considered general enhancers. Recent research shows that the situation is much more complex, and both proteins have been implicated in both positive and negative regulatory pathways (1-4). Exactly how the linker DNA binding proteins exert their regulatory function in transcription remains an enigma (e.g. Ref. 5). They may do so by affecting higher order chromatin structure; in addition, they may act at the level of individual nucleosomes, by creating particles of different stabilities and, hence, different accessibility to binding of general and genespecific transcription factors.The location of linker histones on the nucleosome has been studied for years, albeit with contradictory results (6). Recent studies performed on nucleosomes reconstituted on specific DNA fragments seem to indicate that the linker histone binds highly asymmetrically to the core particle, protecting linker DNA on only one side of the particle (7-9). The choice between two alternative binding sites is probably dictated by DNA sequences in the linker region (8). The location of HMG1, on the other hand, has been so far studied on reconstitutes on only one DNA sequence, the 5 S rDNA from Xenopus borealis (10,11). In this specific case, it was reported that HMG1 interacts with linker DNA in the same way as does histone H1, protecting ϳ5 bp 1 on one side of the nucleosome core and ϳ15 bp on the other side (10, 11).We have demonstrated recently that X. borealis 5 S DNA sequence is not suited for studies involving micrococcal nuclease (MNase) digestion, since results interpreted as "protection" by linker DNA-binding proteins could be obtained with naked DNA and with reconstituted core nucleosomes, in the absence...

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Section: Hmg1 Protection Of Linker Dna 26290contrasting

confidence: 76%

mentioning

confidence: 99%

The Non-histone Chromatin Protein HMG1 Protects Linker DNA on the Side Opposite to That Protected by Linker Histones

Holde

Zlatanova

1998

Journal of Biological Chemistry

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“…We have previously suggested that HMG-D could function as a linker protein in the absence of histone H1 in Drosophila (37). In support of this hypothesis, Wolffe and colleagues (10,38) have postulated a similar role for the Xenopus HMG B1 protein. Thus, as the maternal pool of HMG-D is titrated by the rapid replication and concomitant chromatin assembly and as histone H1 is synthesized, HMG-D would functionally be superseded by histone H1 around mid-blastula transition (37).…”

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confidence: 84%

HMG-D and Histone H1 Interplay during Chromatin Assembly and Early Embryogenesis

Ner¹,

Blank²,

Pérez‐Parallé³

et al. 2001

Journal of Biological Chemistry

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HMG-D is an abundant chromosomal protein associated with condensed chromatin during the first nuclear cleavage cycles of the developing Drosophila embryo. We previously suggested that HMG-D might substitute for the linker histone H1 in the preblastoderm embryo and that this substitution might result in the characteristic less compacted chromatin. We have now studied the association of HMG-D with chromatin using a cellfree system for chromatin reconstitution derived from The vertebrate high mobility group proteins of the HMGB class (formerly termed HMG1/2) (1) are relatively abundant nuclear DNA-binding proteins that bend DNA substantially and appear to act primarily as architectural facilitators in the assembly of nucleoprotein complexes (recently reviewed in Refs. 2-4). There is direct evidence that these proteins facilitate the binding of transcription factors to their cognate sites both in vitro and in vivo, but any involvement in the assembly of histone-DNA complexes is less well documented. Circumstantial evidence indicates that certain functions of the vertebrate HMGB proteins (5-7) may parallel those of the linker histone H1 (8). Both have been shown to bind to linker DNA sequences (7, 9, 10), and both stabilize and bind to four-way junctions (11)(12)(13)(14). HMG-D is one of two Drosophila proteins closely related to the vertebrate HMGB proteins but in contrast to these proteins contains only a single HMG DNA-binding domain (6,15,16). The HMG domain is followed by a region that has basic sequences similar to the C-terminal domain of histone H1 and a short C-terminal acidic stretch also seen in HMGB proteins. The NMR structure of the HMG domain from HMG-D is very similar to the previously determined structure of the B domain of HMG1, which revealed the characteristic L-shaped fold formed by three ␣-helices (17-21).High mobility group proteins of the HMGB family bind DNA with little sequence specificity but recognize structural features in DNA (22-24), including cruciforms, kinks, DNA bulges, and bends (22,23,(25)(26)(27)(28). DNA footprint analysis and mutagenesis experiments suggest that HMG domain proteins bind in the minor groove (29). In addition, both crystallization and NMR studies show that HMG-D bending is achieved by the intercalation of hydrophobic residues at two different base steps (21, 30).The addition of histone H1 protein to an extended array of nucleosome core particles promotes its folding into a fiber with an approximate width of 30 nm (31-33). During early Drosophila development, histone H1 is not detectable (34 -36) until nuclear cycles 7/8 (37). Therefore, H1 is not involved in chromatin condensation in these earliest phases of Drosophila development characterized by rapid condensation-decondensation cycles. We have previously suggested that HMG-D could function as a linker protein in the absence of histone H1 in Drosophila (37). In support of this hypothesis, Wolffe and colleagues (10, 38) have postulated a similar role for the Xenopus HMG B1 protein. Thus, as the maternal pool of H...

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“…Although their force-extension curves do not show a periodic pattern of DNA release (as might be expected of individual nucleosomal disruption events), analysis of the data allowed them to arrive at an Ϸ65 nm (Ϸ190 bp) ''quantization'' in chromatin opening which they attribute to the sudden unwrapping of DNA from individual histone octamers. The abundance of linker histone-like proteins B4, HMG1, HMG2 (8), and other non-histone chromatin-associated proteins in oocyte nuclear extracts used for chromatin assembly in these experiments may in part explain the lack of uniformity and periodicity in the force-extension profiles displayed for chromatin disruption. This lack of uniformity would, in turn, complicate the identification of individual nucleosome disruption signatures.…”

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confidence: 99%

Mechanical disruption of individual nucleosomes reveals a reversible multistage release of DNA

Brower-Toland

Smith

Yeh

et al. 2002

Proc. Natl. Acad. Sci. U.S.A.

447

465

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The dynamic structure of individual nucleosomes was examined by stretching nucleosomal arrays with a feedback-enhanced optical trap. Forced disassembly of each nucleosome occurred in three stages. Analysis of the data using a simple worm-like chain model yields 76 bp of DNA released from the histone core at low stretching force. Subsequently, 80 bp are released at higher forces in two stages: full extension of DNA with histones bound, followed by detachment of histones. When arrays were relaxed before the dissociated state was reached, nucleosomes were able to reassemble and to repeat the disassembly process. The kinetic parameters for nucleosome disassembly also have been determined.

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Evidence for a shared structural role for HMG1 and linker histones B4 and H1 in organizing chromatin.

Cited by 156 publications

References 101 publications

The Non-histone Chromatin Protein HMG1 Protects Linker DNA on the Side Opposite to That Protected by Linker Histones

The Non-histone Chromatin Protein HMG1 Protects Linker DNA on the Side Opposite to That Protected by Linker Histones

HMG-D and Histone H1 Interplay during Chromatin Assembly and Early Embryogenesis

Mechanical disruption of individual nucleosomes reveals a reversible multistage release of DNA

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