[PSI+] prion generation in yeast: characterization of the 'strain' difference

The yeast cytoplasmically-inherited nonsense suppressor [PSI+] determinant is presumed to be a manifestation of the aggregated prion-like state of the Sup35 protein. Overexpression of the Sup35 protein induces generation of [ PSI+] determinants with various suppressor efficiency and mitotic stabiliti es. Here, we demonstrate that the relative frequency of appearance of [PSI] with different properties depends on the SUP35 allele used to induce thei r generation. The difference in properties of [PSI+] determinants was prese rved after their transmission from one yeast strain to another. This differ ence correlated with variation in properties of the Sup35 protein. A novel type of prion instability was observed: some [PSI+] with weak suppressor ef ficiency could convert spontaneously into strong suppressor determinants. C opyright (C) 2001 John Wiley & Sons, Ltd.