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A L Olins

Publications and source records attributed to A L Olins.

54 records · Page 3Linked to original sources
PubMed1978

Physical properties of inner histone-DNA complexes.

Chicken-erythrocyte inner histone tetramer has been complexed with several natural and synthetic DNA duplexes by salt-gradient dialysis at various protein/DNA ratios. The resulting complexes, in low-ionic-strength buffer, have been examined by electron microscopy, circular dichroism, and thermal denaturation. Electron microscopy reveals nucleosomes (nu bodies) randomly arranged along DNA fibers, including poly(dA-dT)-poly(dA-dT), poly(dI-dC)-poly(dI-dC), but not poly(dA)-poly(dT). Circular dichroism studies showed prominent histone alpha-helix and "suppression" of nucleic acid ellipticity (lambda less than 240 nm). Thermal denaturation experiments revealed Tm behavior comparable to that of H1- (or H5-) depleted chromatin. Tm III and Tm IV increased linearly with G + C%(natural DNAs), but were virtually independent of the histone/DNA ratio; therefore, the melting of nucleosomes along a DNA chain is insensitive to adjacent "spacer" DNA lengths. This suggests that Tm III and Tm IV arise from the melting of different domains of DNA associated with the core nu body.

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PubMed1977

Conformational states of chromatin nu bodies induced by urea.

Monomer chromatin nu bodies (nu1) from chicken erythrocyte nuclei were exposed to 0-10 M urea plus 0.2 mM EDTA (PH 7). Alterations in nu1 conformation were examined using hydrodynamic methods (i.e., S, eta, and (formula: see text)), thermal denaturation, circular dichroism, reactivity of histone thiol groups to N-ethyl maleimide, and electron microscopy. The two domains of a nu body (i.e., the DNA-rich shell and the protein-rich core) aeared to respond differently to the destabilizing effects of increasing urea; DNA conformation and stability exhibited noncooperative changes; the core protein structure revealed cooperative destabilization between 4 and 7 M urea. Companion studies on the conformation of the inner histone "heterotypic tetramer" also revealed cooperative destabilization with increasing urea concentration.

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PubMed1976

Ultrastructural features of chromatin nu bodies.

Spread chromatin fibers and isolated chromatin fragments prepared from chicken erythrocyte nuclei were stained with dilute aqueous uranyl acetate. High-resolution electron micrographs reveal two new morphological features exhibited by many of the chromatin nu bodies: (a) lateral association of the nu body with the connecting strand, and (b) a centrally stained spot approximately 15 A wide, possibly corresponding to a hole or crevice within the nu body.

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PubMed1976

Chromatin nu bodies: isolation, subfractionation and physical characterization.

Monomer chromatin subunit particles (nu1) have been isolated in gram quantities by large-scale zonal centrifugation of micrococcal nuclease digests of chicken erythrocyte nuclei. nu1 can be stored, apparently indefinitely, frozen in 0.2 mM EDTA (pH 7.0) at less than or equal to 25 degrees C. Aliquots of the stored monomers have been subfractionated by dialysis against 0.1 M KCl buffers into a soluble fraction containing equimolar amounts of H4, H3, H2A, H2B associated with a DNA fragment of approximately 130-140 nucleotide pairs, and a precipitated fraction containing all of the histones including H5 and H1 associated with DNA fragments. The total nu1 and the KCl-soluble fraction of nu1 have been examined by sedimentation, diffusion, sedimentation equilibrium ultracentrifugation, low-angle X-ray diffraction, and electron microscopy. Physical parameters from all of these techniques are presented and correlated in this study.

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PubMed1975

Urea denaturation of chromatin periodic structure.

Isolated chicken erythrocyte nuclei dispersed in urea solutions (0-5.0 M) have been examined in terms of their low-angle X-ray diffraction and electron microscopic properties. At high urea concentrations, the characteristic low-angle X-ray reflections of chromatin are absent, and the spheroid chromatin particles (v bodies) are markedly perturbed. This lability of chromatin periodic structure to high concentrations of urea is consistent with previous hydrodynamic and spectroscopic studies.

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PubMed1975

Chromatin fragments resembling v bodies.

Fragments of chromatin resembling the spheroid chromatin units (v bodies) have been isolated from formaldehyde-fixed and sonicated chicken erythrocyte nuclei. Ultracentrifugal analyses demonstrated that monomer v bodies have a molecular weight of about 300,000 per particle, exhibit a protein to DNA ratio (by weight) of 1.22:1, and contain a DNA fragment with a molecular weight of approximately 140,000 per v body.

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PubMed1975

Visualization of chromatin substructure: upsilon bodies.

Spread chromatin fibers, from isolated eucaryotic nuclei, reveal linear arrays of spherical particles (upsilon bodies), about 70 A in diameter, connected by thin filaments about 15 A wide. These particles have been observed in freshly isolated nuclei from rat thymus, rat liver, and chicken erythrocytes. In addition, upsilon bodies can be visualized in preparations of isolated sheared chromatin, and in chromatin reconstructed from dissociating solvent conditions (i.e., high urea-NaCl concentration). As a criterion for perturbation of native chromatin structure low-angle X-ray diffraction patterns were obtained from nuclear pellets at different stages in the preparation of nuclei fro electron microscopy. These results suggest that the particulate (upsilon body) structures observed by electron microscopy may be closely related to the native configuration of chromatin.

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PubMed1974

Spheroid chromatin units (v bodies).

Linear arrays of spherical chromatin particles (nu bodies) about 70 angstroms in diameter have been observed in preparations of isolated eukaryotic nuclei swollen in water, centrifuged onto carbon films, and positively or negatively stained. These bodies have been found in isolated rat thymus, rat liver, and chicken erythrocyte nuclei. Favorable views also reveal connecting strands about 15 angstroms wide between adjacent particles.

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PubMed1972

Physical studies of isolated eucaryotic nuclei.

The degree of chromatin condensation in isolated rat liver nuclei and chicken erythrocyte nuclei was studied by phase-contrast microscopy as a function of solvent pH, K(+) and Mg(++) concentrations Data were represented as "phase" maps, and standard solvent conditions selected that reproducibly yield granular, slightly granular, and homogeneous nuclei Nuclei in these various states were examined by ultraviolet absorption and circular dichroism (CD) spectroscopy, low-angle X-ray diffraction, electron microscopy, and binding capacity for ethidium bromide Homogeneous nuclei exhibited absorption and CD spectra resembling those of isolated nucleohistone. Suspensions of granular nuclei showed marked turbidity and absorption flattening, and a characteristic blue-shift of a crossover wavelength in the CD spectra. In all solvent conditions studied, except pH < 2 3, low-angle X-ray reflections characteristic of the native, presumably superhelical, nucleohistone were observed from pellets of intact nuclei. Threads (100-200 A diameter) were present in the condensed and dispersed phases of nuclei fixed under the standard solvent conditions, and examined in the electron microscope after thin sectioning and staining Nuclei at neutral pH, with different degrees of chromatin condensation, exhibited similar binding capacities for ethidium bromide. These data suggest a model that views chromatin condensation as a close packing of superhelical nucleohistone threads but still permits condensed chromatin to respond rapidly to alterations in solvent environment.

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