A correlation between ethidium bromide uptake and petite mutagenesis during the yeast cell cycle.

The intracellular uptake of radioactively labeled ethidium bromide is shown to exhibit a periodic increase at the beginning of each cell cycle in synchronously growing cultures of the yeast, Saccharomyces cerevisiae. These peak rates of ethidium bromide uptake coincide in time with both new rounds of bud formation and the initiation of nuclear DNA synthesis during each cell cycle. Moreover, the peak rates of ethidium bromide uptake are also shown to be correlated in time with the maximum rate of petite mutagenesis induction by this drug during successive cell cycles.