Mutation of the non-Mendelian suppressor, Ψ + , in yeast by hypertonic media

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Abstract
The .psi.+ extrachromosamal determinant in the yeast Saccharomyces cerevisiae suppresses certain UAA markers and increases the efficiency of suppression of UAA markers and increases the efficiency of suppression of UAA suppressors and certain frameshift suppressors. Although the exact nature of .psi.+ determinant is unknown, it is believed to be a self-replicating cytoplasmic factor affecting some component of the translational machinery. In this report growth conditions are described for efficient mutation or elimination of the .psi.+ determinant. Incubation of .psi.+ cultures in hypertonic nutrient medium resulted in rapid conversion to a culture containing predominantly .psi.- cells during the growth cycle. The kinetics of .psi.+ to .psi.- conversion established that the occurrence of .psi.- cells was due to induction and not to selection of pre-existing .psi.- cells. The results suggest that the replication of the .psi.+ determinant is sensitive to hypertonic conditions.