The effect of bleomycin on mitochondrial DNA.

Covalently closed circular mitochondrial DNA (mt-DNA) from mouse fibroblasts (L-cells) forms a separate band from nicked circular or linear DNA molecules in ethidium bromide-cesium chloride byoyant density gradient analysis. The conversion of covalently closed circular mt-DNA to nicked circular or linear DNA may serve as a sensitive method of detecting DNA strand breaks induced by bleomycin (BLM). At a very high concentration BLM induces the conversion of closed circular mt-DNA to nicked circular or linear DNA, however even after 24 h of exposure to BLM at a high concentration a considerable amount of closed circular mt-DNA molecules remains intact.