C-terminal truncation of the Sup35 protein increases the frequency of de novo generation of a prion-based [PSI+] determinant in Saccharomyces cerevisiae.

The yeast non-Mendelian [PSI+] determinant is presumed to be the manifestation of the aggregated prion-like state of the Sup35 protein. Plasmid-mediated amplification of the SUP35 gene greatly increases the frequency of Sup35p transition to this prion-like state. Here we show that the 3'-deletions of plasmid SUP35, leading to the C-terminal truncation of Sup35p, further increase the frequency of [PSI+] induction despite a marked decrease in Sup35p expression levels. The data suggest that the presence of Sup35p N-terminal proteolytic fragments can cause [PSI+] appearance in wild-type yeast cells.