Factors affecting petite induction and the recovery of respiratory competence in yeast cells exposed to ethidium bromide

Summary

When growing cultures of S. cerevisiae are treated with high concentrations of ethidium bromide (>50 μg/ml), three phases of petite induction may be observed: I. the majority of cells are rapidly converted to petite, II. subsequently a large proportion of cells recover the ability to form respiratory competent clones, and III. slow, irreversible conversion of all cells to petite. The extent of recovery of respiratory competence observed is dependent on the strain of S. cerevisiae employed and the temperature and the carbon source used in the growth medium. The effects of 100 μg/ml ethidium bromide are also produced by 10 μg/ml ethidium bromide in the presence of the detergent, sodium dodecyl sulphate, and recovery is also observed when cells are treated with 10 μg/ml ethidium bromide under starvation conditions. Genetic analysis of strain differences indicates that a number of nuclear genes influence petite induction by ethidium bromide.

In one strain, S288C, petite induction by 100 μg/ml ethidium bromide is extremely slow under certain conditions. Mitochondria isolated from S288C lack the ethidium bromide stimulated nuclease activity found in D243-4A, a strain which shows triphasic kinetics of petite formation. This enzyme may, therefore, be responsible for the initial phase of rapid petite formation.