Ionic strength‐dependent conformational transitions of chromatin. Circular dichroism and thermal denaturation studies

Fulmer, Andrew W.; Fasman, Gerald D.

doi:10.1002/bip.1979.360181115

Cited by 51 publications

(46 citation statements)

References 54 publications

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“…cm2 . dmol-') reported by Fasman et al [20,21] may be related to the biphasic melting profiles obtained by the authors. The extracted DNAs show a high degree of purity, as judged by electrophoresis in polyacrylamide gel gradients (2.4-8.5 "/,).…”

Section: Preparation and Characterization Of' Chromatin Oligomerssupporting

confidence: 60%

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Conformation of Chromatin Oligomers

Marion¹,

Bezot²,

Hesse-Bezot³

et al. 1981

European Journal of Biochemistry

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Quasielastic laser light scattering measurements have been made on chromatin oligomers to obtain information on the transition in their electrooptical properties, previously observed for the hexameric structures [Marion, C. and Roux, B. (1978) Nucleic Acids Res. 5, 4431 -44491. Translational diffusion coefficients were determined for mononucleosomes to octanucleosomes containing histone HI over a range of ionic strength. At high ionic strength, oligomers show a linear dependence of the logarithm of diffusion coefficient upon the logarithm of number of nucleosomes. At low ionic strength a change occurs between hexamer and heptamer. Our results agree well with the recent sedimentation data of Osipova et al. [Eur. J . Biochem. (1980) 113, 183 -1881 and of Butler and Thomas [J. Mol. Biol. (1980) 140, 505-5291 showing a change in stability with hexamer. Various models for the arrangements of nucleosomes in the superstructure of chromatin are discussed. All calculations clearly indicate a conformational change with the hexanucleosome and the results suggest that, at low ionic strength, the chromatin adopts a loosely helical structure of 28-nm diameter and 22-nm pitch. These results are also consistent with a discontinuity every sixth nucleosome, corresponding to a turn of the helix. This discontinuity may explain the recent electric dichroism data of Lee et al. [Biochemistry (1981) 20, 1438 -14451. The hexanucleosome structure which we have previously suggested, with the faces of nucleosomes arranged radially to the helical axis has been recently confirmed by Mc Ghee et al. [Cell (1980) 22, 87-96]. With an increase of ionic strength, the helix becomes more regular and compact with a slightly reduced outer diameter and a decreased pitch, the dimensions resembling those proposed for solenoid models.A detailed knowledge of the structural organization of chromatin is required to understand the mechanisms involved in gene expression. In order to account for the highly condensed state of chromosomes, the chromatin is organized into higher-order structures whose diameter (20 -30 nm) is about twice that of nucleosomes, the basic chromatin units (for reviews see [I]). It is not clear how nucleosome chains are folded or coiled in the chromosome fiber and this packing of nucleosomes has been discussed in terms of either solenoidal structure or helical arrays having about 6 -10 nucleosomes per turn, or of 'superbeads' or 'clustered arrays' containing several nucleosomes. The evidence in favour of superbeads has. however, been questioned recently [ 2 ] . Much of the data supporting these models comes from electron microscopy and it appeared recently that this technique may be subject to possible artefacts, especially at low ionic strengths [3 -51. Evidence from other methods is thus needed. In previous papers [6,7], we reported transient electric birefringence studies of rat liver chromatin oligomers. They showed a change in conformation with hexamer. This result is confirmed by recent sedimentation data [5] and birefringence ...

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Section: Preparation and Characterization Of' Chromatin Oligomerssupporting

confidence: 60%

“…(----) The degree of compactness of oligonucleosomes and higherorder structures is sensitive to the salt concentration [3,5,20,29,. The decrease of the ionic strength produces an increase in volume and then opposite effects on D (decrease) and s (increase).…”

Section: Kirk Wood Theorzyfor Translational Properties Of Assembliesmentioning

confidence: 99%

Conformation of Chromatin Oligomers

Marion¹,

Bezot²,

Hesse-Bezot³

et al. 1981

European Journal of Biochemistry

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“…The samples of chromatin fractions were thermally denatured in 0.01 SSC (1 X SSC -0.15 AL NaCl, 0.015 M trisodium citrate, pH 7.0) as described earlier [10]. Peaks, which correspond to the thermal transitions of free DNA and of nucleosomes, were identified according to Defer et al [11] and Fulmer and Fasman [12].…”

Section: Methodsmentioning

confidence: 99%

Age-Related Changes of Supranucleosomal Structures and DNA-Synthesizing Properties of Rat Liver Chromatin

Tg¹,

Vn²,

Levitsky³

et al. 1991

Gerontology

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The template activity, nucleosomal pattern and thermodenaturation parameters of transcriptionally low active (TLA) and transcriptionally active liver chromatin fractions were studied in adult (6–8 months) and old (26–28 months) rats. The following age-related changes of chromatin template properties were found: decrease of endogenous DNA polymerase α- and β-activity in vitro in both chromatin fractions, and redistribution of newly synthetized RNA between mono- and oligonucleosomes in the TLA fraction. These changes are thought to be connected with age-related reorganization of chromatin structure, i.e. with increase of DNA-protein interactions, which stabilize association of chromatin supranucleosomal structures.

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“…A similar pattern of behavior has been reported by McCleary and Fasman though with different melting temperatures, presumably resulting from different solution conditions [38]. A comparison [39] of the melting profiles of the core particle, and of HI-depleted and H5-depleted compact dimers and trimers shows that along the series the size of the premelt region at about 60°C decreases, the temperature of the main melt increases from 75 "C for the core particle to 79 "C for the dimer and 81 "C for the trimer, and for the dimer and trimer a new transition is observed at about 73 "C. This approximates to the melting profiles of chromatin which showed a weak inflection at about 57 -62 "C for the premelt followed by two transitions at 72 -74 "C and 82 -84 "C of increasing magnitude [24,29]. In this study, the melting profiles have been compared of mononucleosomes, dinucleosomes and trinucleosomes from highly acetylated and control chromatin.…”

mentioning

confidence: 63%

Thermal Denaturation Studies of Acetylated Nucleosomes and Oligonucleosmes

Yau

Thorne

Imai

et al. 1982

European Journal of Biochemistry

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The thermal melting behaviors of control and acetylated mononucleosomes, dinucleosomes and trinucleosomes have been studied. Along each series of oligonucleosomes, the melting profiles change in a manner consistent with the increasing number of nucleosomes. For the control mononuclecrsome, the melting profile exhibits a premelting region at about 61 -64°C and a major cooperative transition at 75-77 "C. The melting profiles of the control dinucleosomes and trinucleosomes show a premelt at 61 -62 "C (similar to that of the nucleosome core) ; an intermediate transition at 73 -74 "C for the dinucleosome and at 76 -77 "C for the trinucleosome and a major cooperative transition at 79-80 "C for the dinucleosome and at 81 -82 "C for the trinucleosome. The major cooperative transition at the hignest melting temperatures in the melting profiles of the mononucleosome, dinucleosome and trinucleosome comes from the melting of the central region of DNA in the nucleosome strongly complexed with the core histones; the premelt region is attributed to two DNA segments per nucleosome which flank this central DNA region and are free or weakly complexed with histones. The origin of the intermediate transition found for the dinucleosomes and trinucleosomes is not fully understood but probably results from the melting of DNA at the entry to and exit from the nucleosome and the linker D N A which are complexed with histones. A very similar pattern of behavior is observed for the acetylated oligonucleosomes. Direct comparison of the melting profiles of acetylated and control mononucleosomes, dinucleosomes and trinucleosoines show that the premelt region is unaffected by histone acetylation whereas the intermediate and major cooperative transitions for the acetylated oligonucleosomes are broader and occur consistently at lower temperatures than for the controls. These differences support proposals that the N-terminal regions of core histones interact within the nucleosome and on linker DNA. Now that we have an outline understanding of the structure of the nucleosome at low resolution [I -31 and of the packing of nucleosomes in extended and supercoiled chromatin [4 -91, attention is directed to the role of histone acetylation on the structure and function of transcriptionally active or competent chromatin. Allfrey et al. [lo] first correlated one of the requirements of transcriptional activity with histone acetylation and this correlation has been found to hold for enhanced transcriptional activity induced by hormones or drugs (see [I I]). Cell cycle studies of histone H4 acetylation show a strong correlation between the behavior of tetraacetylated H4 and transcriptional activity [I 21. Yeast chromatin, which has a very high overall level of transcriptional activity, has been found to contain 63% of diacetylated, triacetylated and tetraacetylated histone H4 [13].There are four sites of reversible acetylation of lysines in histones H2B, H3 and H4 and one site in histone H2A. All of these sites are located in the N-terminal quarters of the...

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Ionic strength‐dependent conformational transitions of chromatin. Circular dichroism and thermal denaturation studies

Cited by 51 publications

References 54 publications

Conformation of Chromatin Oligomers

Conformation of Chromatin Oligomers

Age-Related Changes of Supranucleosomal Structures and DNA-Synthesizing Properties of Rat Liver Chromatin

Thermal Denaturation Studies of Acetylated Nucleosomes and Oligonucleosmes

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