FRACTIONATION OF THE NUCLEUS BY DIVALENT CATIONS

0.3–0.5 M MgCl2 was used to disassemble nuclei and to isolate by a single centrifugation in less than 3 hr a nuclear envelope fraction in 55–60% yield as assessed by phospholipid recovery. Its gross chemical composition was determined and its morphology was studied electron microscopically by sectioning, freeze etching, and negative staining procedures.