Configuration of unsheared nucleohistone. Effects of ionic strength and of histone F1 removal

Lewis, Edwin A.; DeBuysere, Michael S.; Rees, Allan W.

doi:10.1021/bi00646a029

Cited by 43 publications

(19 citation statements)

References 36 publications

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“…is more highly condensed than chromatin isolated by convenby simple subtional methods (7,12,13). The condensed chromatin samples is a single negexhibit low-magnitude CD spectra.…”

Section: Resultsmentioning

confidence: 99%

“…The CD spectrum of DNA in chromatin is substantially reduced in intensity relative to protein-free DNA. There is some variability in the reported extent of this alteration (7,(10)(11)(12)(13). For isolated core particle mononucleosomes, reports agree that the CD spectrum shows a maximum ellipticity which is less than onefourth that of protein-free DNA (8,14,15).…”

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confidence: 99%

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Circular dichroism analysis of mononucleosome DNA conformation.

Cowman¹,

Fasman²

1978

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

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Mononucleosomes were isolated from micrococcal nuclease digests of chicken erythrocyte nuclei. The circular dichroism properties of mononucleosome preparations, differing in average DNA length and in Hi and H5 content, demonstrate that the spectrum of chromatin is due only to the complete structure of its repeating subunits. The nucleoprotein spectra are all altered relative to rotein-free DNA by the emergence of a single negative band at 275 nm, similar to the band observed for * DNA. The intensity of the +-type band depends on the prop rtion of DNA condensed in a specific manner. The *-type and is proposed to be due to the compact DNA tertiary structure; i.e., the manner in which the DNA is wound around the histone core allowing interactions between adjacent turns of the superhelix. This interpretation attributes changes and variability in nucleoprotein circular dichroism spectra under different experimental conditions to alterations in DNA tertiary structure rather than secondary structure. Evidence has been accumulated that indicates that the folding of DNA in chromatin involves several levels of organization. First, DNA is condensed by a histone octamer into compact subunits, or nucleosome cores. The cores contain approximately 140 base pairs of DNA and two each of the histones H2A, H2B, H3, and H4 (for reviews see refs. 1 and 2). The cores are connected by "linker" DNA regions, the lengths of which are variable and with which the very lysine-rich histone H1 (and H5 in avian erythrocytes) interacts. This level of DNA organization corresponds to the "beads-on-a-string" structure (3). The second level of organization is the 100-A nucleofilament, in which adjacent nucleosome cores are presumably in contact, and the linker DNA is condensed (3-5). The third level of organization is the 250 to 300-A diameter chromatin fiber, proposed to be a solenoidal arrangement of the 100-A nucleofilament (4-7). The second and third organizational levels depend on the presence of H1 and/or salts (4-6).We have been interested in the possibility that the circular dichroism (CD) spectrum of DNA is sensitive not only to changes in secondary structure (base tilt, twist, etc.), but also to the higher levels of DNA organization in chromatin (8,9). In the latter case, the DNA secondary structure could remain within the B family of conformations, but the change in tertiary structure might result in an altered CD spectrum. The CD spectrum of DNA in chromatin is substantially reduced in intensity relative to protein-free DNA. There is some variability in the reported extent of this alteration (7, 10-13). For isolated core particle mononucleosomes, reports agree that the CD spectrum shows a maximum ellipticity which is less than onefourth that of protein-free DNA (8,14,15). The overall reductions in ellipticity measured for both chromatin and mononucleosome core particles are accompanied by subtle changes in band shape and wavelength in the spectra.We have examined the CD properties of mononucleosomes having varying linker DNA le...

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“…is more highly condensed than chromatin isolated by convenby simple subtional methods (7,12,13). The condensed chromatin samples is a single negexhibit low-magnitude CD spectra.…”

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

Circular dichroism analysis of mononucleosome DNA conformation.

Cowman¹,

Fasman²

1978

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

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“…A year earlier, Rees at al. (4,5) had obtained chromatin in a similar manner and observed very high sedimentation coefficients combined with fairly low intrinsic viscosities. An unusual property of their material was its solubility in 0.15 M buffers; this solubility was lost, however, after the chromatin had been sheared.…”

Section: Introductionmentioning

confidence: 84%

Studies on the structure of isolated chromatin in three different solvents

et al. 1979

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Properties of calf thymus chromatin, prepared by mild procedures, have been studied in various solvents. In 0.2 mM EDTA s-values ranged from 20 to 30 S and intrinsic viscosities from 5 to 24 dl/g. Dialysis against 0.15 M NaCl or 0.2 mM MgCl2 changed these values to 80 to 100 S and 0.2 to 5 dl/g, respectively, indicating an essentially more compact structure. In 0.2 mM EDTA X-ray scattering yielded a cross section diameter of 9 nm, which is associated with the tertiary structure of chromatin fiber (M/L = 21200 Dalton/nm). By dialysis against 0.15 M NaCl or 0.2 mM MgCl2 part of the material spontaneously formed quarterny structures (cross section diameters 25-29 nm). The rest of the material with cross section diameters less than 9 nm is supposed to be more strongly sheared tertiary structure which seems to be unable to form quarterny structure due to artificial conformational changes.

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“…The hydrodynamic data bear this out . On increasing ionic strength, the sedimentation constant increases and the viscosity decreases (25) but the rate of increase of sedimentation constant is much greater for H 1containing chromatin than for HI-depleted chromatin ( Fig. 4 in reference 38) .…”

Section: Condensation Ofhl -Depleted Chromatinmentioning

confidence: 97%