title: DNA supercoiling by Xenopus laevis oocyte extracts: requirement for a nuclear factor.
abstract: A purified system is described for the introduction of negative supercoils into simian virus 40 DNA. The system consists of histones H2A, H2B, H3, and H4, DNA-relaxing enzyme, and a purified factor from Xenopus laevis stage 6 oocyte nuclei. The nuclei are prepared en masse by the technique of F. Scalenghe, M. Buscaglia, C. Steinheil, and M. Crippa [(1978) Chromosoma 60, 299-308]. The supercoiled simian virus 40 DNA prepared by this method is indistinguishable from simian virus 40 supercoiled DNA prepared from infected monkey cells.
mesh_terms: D000818:Animals; D002467:Cell Nucleus; D004264:DNA Topoisomerases, Type I; D004278:DNA, Superhelical; D004279:DNA, Viral / Q000235:genetics*; D005260:Female; D006657:Histones; D009865:Oocytes; D013539:Simian virus 40 / Q000235:genetics; D014981:Xenopus / Q000235:genetics*
chemical_list: D004278:DNA, Superhelical; D004279:DNA, Viral; D006657:Histones; D004264:DNA Topoisomerases, Type I