Electron microscopic observation of mitochondrial DNA isolated from a human kidney: circular dimers in histologically normal organ mitochondria

Circular DNA isolated from human kidney mitochondria was studied by electron microscopy. I. Mean contour length of monomers of the mitochondrial DNA was 4.96 ± SE 0.28 /μ 2. The complex molecules (oligomers) of mitochondrial DNA were observed in frequency of 6.2 per cent. Among them circular dimers accounted for two per cent of all circular DNA molecules. 3. Circular DNA fibers with an intermediate perimeter between the　monomer and dimer, and with a contour length shorter than 3 μ were occasionally observed. 4. Some discussions were made on the emergence of the circular dimer.