[Damage by gamma rays and heavy ions to superhelical structures of nuclear DNA]

Chinese hamster cells (V79-4), human lymphocytes and mouse ascites cell were exposed to gamma-rays and heavy ions (4He and 12C). Sedimentation of complexes containing DNA was studied after cell lysis by centrifugation in a neutral sucrose gradient. The distinctions noted after irradiation with gamma-rays and heavy ions are consistent with the idea of the superhelical organization of DNA into discrete and membrane-bound compact units. According to the estimates made the diameter of these complexes was approximately 0.2 micron and DNA content, about 2 X 10(9) dalton.