THE HISTONE H3/H4.N1 COMPLEX SUPPLEMENTED WITH HISTONE H2A-H2B DIMERS AND DNA TOPOISOMERASE-I FORMS NUCLEOSOMES ON CIRCULAR DNA UNDER PHYSIOLOGICAL CONDITIONS

  • 25 August 1990
    • journal article
    • research article
    • Vol. 265  (24) , 14487-14496
Abstract
We have fractionated the whole cell extract of Xenopus oocytes (oocyte S-150) and isolated the endogenous components required for DNA supercoiling and nucleosome formation. Histone H2B and the three oocyte-specific H2A proteins were purified as free histones. Histones H3 and H4 were purified 100-fold in a complex with the acidic protein N1. In the presence of DNA topoisomerase I or II, histone H3/H4.cntdot.N1 complexes supercoil DNA in a reaction that is inhibited by Mg2+, and this inhibition is relieved by NTPs. The supercoiling reaction induced by H3/H4.cntdot.N1 complexes is enhanced by free histone H2A-H2B dimers, which by themselves do not supercoil DNA. Nuclease digestions and protein analyses indicate that H3/H4.cntdot.N1 complexes form subnucleosomal particles containing histones H3 and H4. Nucleosomes containing 146-base pair DNA and the four histones are formed when histones H2A and H2B complement the reaction.