Comparison of Physicochemical Properties of Mitochondrial and Nuclear Deoxyribonucleic Acid from Rat Liver Cells

THE discovery of deoxyribonucleic acid (DNA) in mitochondria 1–9 has opened the way for investigations of the long-standing problem of extra-genome cytogenetic determinants. DNA fibres have been found in mitochondria from tissues belonging to various different classes of animals 1 . The principal difficulty to be dealt with in the isolation of mitochondrial DNA is caused by the necessity of separating the soluble nuclear DNA, adsorbed on the surface of mitochondria. For this purpose we used a method of purification of mitochondria in ‘Urographin’ density gradient 8 or treatment of the mitochondrial fraction with DNase (150 µg/ml. for 1.5 h at 0° C). Fibres of high-polymer deproteinized DNA were obtained by means of the phenol method after Kirby 10 and Marmur 11 . The average DNA content in liver mitochondria amounted to 0.65 µg/mg protein.