Fig. 3. Southern blot analysis of total DNAs extracted from Ax-2 cells and cells treated with 30 µg/ml of EtBr for 40 hours. The DNAs were digested with the indicated restriction enzymes and electrophoresed. After transfer of the size-fractionated DNA fragments to nylon membranes, they were hybridized with the 32P-labeled (A) nuclear DNA-specific probe Dd-trap1 or (B) mtDNA-specific probe rps4, followed by autoradiography.