Effect of Nucleoplasmin on a Nucleosome Structure.

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  • Iihara Akiko
    Laboratory of Bio-Material Chemistry, Division of Bioscience, Graduate School of Environmental Earth Science, Hokkaido University
  • Sato Koji
    Laboratory of Bio-Material Chemistry, Division of Bioscience, Graduate School of Environmental Earth Science, Hokkaido University
  • Hozumi Kentaro
    Laboratory of Bio-Material Chemistry, Division of Bioscience, Graduate School of Environmental Earth Science, Hokkaido University
  • Yamada Masanori
    Laboratory of Bio-Material Chemistry, Division of Bioscience, Graduate School of Environmental Earth Science, Hokkaido University Faculty of Textile Science and Technology, Shinshu University
  • Yamamoto Hiroyuki
    Faculty of Textile Science and Technology, Shinshu University
  • Nomizu Motoyoshi
    Laboratory of Bio-Material Chemistry, Division of Bioscience, Graduate School of Environmental Earth Science, Hokkaido University
  • Nishi Norio
    Faculty of Textile Science and Technology, Shinshu University

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Abstract

Nucleoplasmin, isolated from the Xenopus laevis egg, was the first protein defined as a molecular chaperone. DNA forms a nucleosome structure with histones in eucaryotic somatic cells. Nucleoplasmin promotes the assembly of the nucleosome structure. We have now determined the effect of nucleoplasmin on the structure of the nuclease digested-nucleohistone (d-NH). The d-NH was prepared from nucleohistone by treatment with micrococcal nuclease. The DNA of the d-NH showed 200 bp ladder bands on an agarose gel electrophoresis. The Circular dichroism spectra of nucleohistone demonstrated an α-helical structure with spectra minima at 208 and 222 nm, while that of the d-NH showed a minimum peak at 228 nm. The turbidity of d-NH was found to be higher than that of nucleohistone, suggesting that d-NH was aggregated. The aggregation was inhibited by an addition of NaCl. Furthermore, guanidine HCl reduced the d-NH aggregation, while urea did not affect the aggregation. These results suggest that hydrogen bonds and/or ionic charges were mainly involved in the aggregation. When nucleoplasmin was added to a solution of d-NH, the mixtures possessed an α-helical conformation. Poly-l-glutamic acid was also found to inhibit the aggregation and to promote the formation of α-helical structures, however, this was not as effective as of nucleoplasmin. The conformational thermal stability of the nucleoplasmin/d-NH mixture was higher than that of d-NH alone. These results indicate that nucleoplasmin inhibits aggregation of d-NH and increases the α-helical structure of the core histones. Nucleoplasmin seems to play a critical role in the nucleosome assembly as a molecular chaperone by inhibiting the aggregation of histone and DNA. These data define the molecular mechanisms of the nucleosome assembly by nucleoplasmin.

Journal

  • Polymer Journal

    Polymer Journal 34 (3), 184-193, 2002

    The Society of Polymer Science, Japan

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