In Vitro Propagation of the Prion-Like State of Yeast Sup35 Protein

Abstract

The yeast cytoplasmically inherited genetic determinant [ PSI + ] is presumed to be a manifestation of the prion-like properties of the Sup35 protein (Sup35p). Here, cell-free conversion of Sup35p from [ psi − ] cells (Sup35p psi − ) to the prion-like [ PSI + ]-specific form (Sup35p PSI + ) was observed. The conversion reaction could be repeated for several consecutive cycles, thus modeling in vitro continuous [ PSI + ] propagation. Size fractionation of lysates of [ PSI + ] cells demonstrated that the converting activity was associated solely with Sup35p PSI + aggregates, which agrees with the nucleation model for [ PSI + ] propagation. Sup35p PSI + was purified and showed high conversion activity, thus confirming the prion hypothesis for Sup35p.