Petite induction in yeast, Saccharomyces cerevisiae, by phenanthridinium compounds: promotive effects of propidium iodide on mutagenesis by ethidium bromide or 8-deaminoethidium chloride.

Abstract

Promotive effects of propidum iodide (PI) on petite induction by 8-deaminoethidium chloride (8-DAEC) were examined. 8-DAEC was a potent petite inducer in growing yeast cells but not in resting yeast cells. Addition of PI promoted the petite induction by 8-DAEC throughout the cultivation time at a concentration that was ineffective by itself. In resting cells, petites were scarcely induced by either 8-DAEC or PI or both, even after prolonged incubation. Notable sectored colony induction was observed after prolonged incubation of the yeast cells with either 8-DAEC or PI in phosphate·buffer. The petite induction by ethidium bromide (EB) was not accelerated but was delayed in PI-pretreated cells, whereas the simultaneous presence of PI promoted the EB mutagenesis.These results suggested that the simultaneous presence of PI and petite inducer in growth medium was required in order to exhibit the promotive effects. Possible mechanisms of the differences in the process of petite induction between resting and growing cells are discussed.