Species barrier in yeast [PSI⁺] prion transmission

Abstract

The Sup35 protein of Saccharomyces cerevisiae is a eukaryotic polypeptide release factor (eRF3), which is necessary for terminating protein synthesis at stop codons. The aggregated form of Sup35, which is referred to as the [PSI⁺] element, self-propagates and is transmitted cytoplasmically in the manner of the “protein-only” transmission of mammalian prion diseases. In [PSI⁺] cells, most of the Sup35 is converted from a soluble, active state into an insoluble, inactive state similar to the mammalian prion amyloid. As with mammalian prions, a species barrier prevents prion transmission between yeast species. The N-terminal of Sup35 of Saccharomyces cerevisiae, necessary for [PSI⁺], contains two species-signature elements — a Gln/Asn-rich region (residues 1–41; designated NQ) that is followed by oligopeptide repeats (designated NR).