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 sv 40 DNA. The system consists of histones H2A, H2B, H3 and H4, DNA-relaxing enzyme, and a purified factor from X. laevis stage 6 oocyte nuclei. The nuclei are prepared en masse by the technique of F. Scalenghe, et al (1978). The supercoiled sv-40 DNA prepared by this method is indistinguishable from sv-40 supercoiled DNA prepared from infected African green monkey [cv-1] cells.