Reversion analysis of [psi−] mutations inSaccharomyces cerevisiae

Abstract

SUMMARY: Mutants of [psi] a cytoplasmically inherited factor in the yeastSaccharomyces cerevisiaewere isolated after treatment with a variety of agents including conventional mutagens and a number of compounds which cause loss of [psi] at high frequencies, namely methanol, KCl, dimethyl sulphoxide and guanidine hydrochloride. In [psi⁻] mutants the suppressorSUQ5does not suppress ochre mutations such asade.2.1.Reversion analysis of the [psi⁻] mutants revealed three classes: (1) a class of agents producing [psi⁻] mutations which could readily revert to [psi⁺] (methanol, KCl and dimethyl sulphoxide belong to this class), (2) those which could not be shown to revert (GuHCl) and (3) the conventional mutagens which produced both revertible and apparently non-revertible [psi⁻] mutations. We conclude that GuHCl causes a deletion or loss of the [psi] factor. Methanol may cause an alteration of ‘state’ for example, of a promoter, and KCl may be selecting or inducing low copy number variants of [psi⁺] strains. It is possible that DMSO may be involved in regulation of [psi].