Chimeric Yeast Prions with Unstable Inheritance

The Saccharomyces cerevisiae [PSI] factor, a cytoplasmic omnipotent nonsense suppressor, is a conformationally changed (prion) form of translation termination factor eRF3 (Sup35p). Induction and maintenance of the [PSI] factor depend on the prionizing peptide located in the N domain of Sup35p. The N domain of Sup35p was fused with phosphoribosylaminoimidazole carboxylase (Ade2p), a purine biosynthesis enzyme, and the hybrid protein (NM-Sup35p::Ade2p) was tested for induction of the [PSI] factor. Transformation with a centromeric plasmid carrying the gene for NM-Sup35p::Ade2p induced a [PSI]-like factor in yeast cells, which was evident from efficient nonsense suppression. The suppressor effect depended on the presence of the prionizing peptide both in the hybrid protein and in Sup35p synthesized from the chromosomal gene, as well as on the presence of the prion-like [PIN] factor in the cell.