Translation termination efficiency can be regulated in Saccharomyces cerevisiae by environmental stress through a prion-mediated mechanism

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Abstract
[PSI+] is a protein‐based heritable phenotype of the yeast Saccharomyces cerevisiae which reflects the prion‐like behaviour of the endogenous Sup35p protein release factor. [PSI+] strains exhibit a marked decrease in translation termination efficiency, which permits decoding of translation termination signals and, presumably, the production of abnormally extended polypeptides. We have examined whether the [PSI+]‐induced expression of such an altered proteome might confer some selective growth advantage over [psi−] strains. Although otherwise isogenic [PSI+] and [psi−] strains show no difference in growth rates under normal laboratory conditions, we demonstrate that [PSI+] strains do exhibit enhanced tolerance to heat and chemical stress, compared with [psi−] strains. Moreover, we also show that the prion‐like determinant [PSI+] is able to regulate translation termination efficiency in response to environmental stress, since growth in the presence of ethanol results in a transient increase in the efficiency of translation termination and a loss of the [PSI+] phenotype. We present a model to describe the prion‐mediated regulation of translation termination efficiency and discuss its implications in relation to the potential physiological role of prions in S.cerevisiae and other fungi.