Restriction fragment length polymorphism (RFLP) analysis provides evidence for a high degree of homology of mitochondrial DNAs from rat hepatomas versus normal rat livers.

Where differences have been reported between tumor and normal mitochondrial DNA (mtDNA), they have generally involved limited modifications of the genome (Taira et al., Nucleic Acids Res. 11:1635, 1983; Shay and Werbin, Mutat. Res. 186:149, 1987). However, Corral et al. (Nucleic Acids Res. 16:10935, 1988; 17:5191, 1989) observed recombination between cytochrome oxidase subunit I (COI) and NADH dehydrogenase subunit 6 (ND6), two genes normally on opposite sides of the circular mitochondrial genome. In rat hepatoma mtDNA COI and ND6 were reported to be separated by only 230 base pairs (Corral et al., 1988, 1989). We have performed RFLP analysis on mtDNA from normal rat livers and rat hepatomas, using COI and ND6 probes. Additional experiments compared end-labeled DNA fragments produced by EcoRI and HindIII digestion of mtDNA. These studies failed to provide any evidence for genetic recombination in rat hepatoma mtDNA, even in the same cell line used by Corral et al. Rather, they support the conclusion that mtDNA from tumor and normal tissues exhibits a low degree of heterogeneity.