Differential effect of ethidium bromide and cytosine arabinoside on mitochondrial and nuclear DNA synthesis in HeLa cells.

The effect of ethidium bromide (EB) on the synthesis of circular DNA of mammalian cells was studied by isopycnic centrifugation in a CsCl-EB solution. EB (0.1 —0.5 ^wg/ml) interferes with the synthesis of newly-formed circular D N A of HeLa cell mitochondria and causes degradation of the pre-existing circular DNA, as well. Under the same conditions, nuclear DNA synthesis was not inhibited. This effect was not reversible at a concentration of 0.5 /ug EB/ml or more. Cytosine arabinoside (ara-C) did not exhibit an effect similar to that of EB.