Induction of respiratory deficient mutants in Saccharomyces cerevisiae by mono- and diazido analogs of ethidium.

Mono- and diazido analogs of ethidium when photolyzed with yeast cells were highly effective in inducing respiratory deficient (RD) mutants. The monoazide was more mutagenic, though slightly less photosensitive, and under the concentrations and conditions used, both required photolysis to be significantly mutagenic. Ethidium bromide (EB) competed with either its mono- or diazide analog for RD induction when applied before, but not after, the photolysis step. This suggested that the initial mutagenic binding sites for azides were identical with those of EB. There was no self-rescue or recovery in azide mutagenesis in contrast to EB. Furthermore, recovery from azide mutagenesis could not be provoked by EB. This confirmed a simple competition between binding of EB and its azide analogs to account for the prevention by EB of the azide induced mutations.