Fractionation of the nucleus by divalent cations. Isolation of nuclear membranes

0.3-0.5 M MgCl(2) 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.