C-TERMINAL TRUNCATION OF THE SUP35 PROTEIN INCREASES THE FREQUENCY OFDE-NOVO GENERATION OF A PRION-BASED [PSI-CEREVISIAE(] DETERMINANT IN SACCHAROMYCES)

The yeast non-Mendelian [PSI+] determinant is presumed to be the manif estation of the aggregated prion-like state of the Sup35 protein. Plas mid-mediated amplification of the SUP35 gene greatly increases the fre quency of Sup35p transition to this prion-like state. Here we show tha t the S'-deletions of plasmid SUP35, leading to the C-terminal truncat ion of Sup35p, further increase the frequency of [PSI+] induction desp ite a marked decrease in Sup35p expression levels. The data suggest th at the presence of Sup35p N-terminal proteolytic fragments can cause [ PSI+] appearance in wild-type yeast cells.