Effect of ethidium bromide on mitochondrial DNA and cytochrome synthesis in HeLa cells

The effect of ethidium bromide (EB) on the synthesis of covalently closed circular DNA in HeLa cells and on the DNA of isolated HeLa cell mitochondria was studied.When HeLa cells were exposed to EB at a concentration of 0.1 μg/ml or higher for 48 h, newly synthesized mitochondrial DNA could not be detected by isopycnic centrifugation in CsCl-EB solution. Nuclear DNA synthesis was not decreased. Cell growth was inhibited by approximately 10%. Synthesis of cytochromes was increased in treated cells.At concentrations of 0.1 μg/ml, incorporation of ³H-thymidine into the DNA of isolated mitochondria was completely inhibited and at concentrations of 0.01 and 0.001 μg/ml, it was lowered by 40–50%.