PRION-INDUCING DOMAIN-2-114 OF YEAST SUP35 PROTEIN TRANSFORMS IN-VITRO INTO AMYLOID-LIKE FILAMENTS

The yeast non-Mendelian genetic factor [PSI], which enhances the effic iency of tRNA-mediated nonsense suppression in Saccharomyces cerevisia e, is thought to be an abnormal cellular isoform of the Sup35 protein, Genetic studies have established that the N-terminal part of the Sup3 5 protein is sufficient for the genesis as well as the maintenance of [PSI]. Here we demonstrate that the N-terminal polypeptide fragment co nsisting of residues 2-114 of Sup35p, Sup35pN, spontaneously aggregate s to form thin filaments ht vitro, The filaments show a beta-sheet-typ e circular dichroism spectrum, exhibit increased protease resistance, and show amyloid-like optical properties, It Is further shown that fil ament growth in freshly prepared Sup35pN solutions can be induced by s eeding with a dilute suspension of preformed filaments, These results suggest that the abnormal cellular isoform of Sup35p is an amyloid-lik e aggregate and further indicate that seeding might be responsible for the maintenance of the [PSI] element in vivo.