Pearls Environmental Regulation of Prions in Yeast

The term prion, proteinaceus infectious particle, was first used to describe the causative agent of a group of mammalian neurodegenerative diseases known as transmissible spongiform encephalopathies (TSEs) [1]. The mammalian prion protein (PrP) can exist in either a normal cellular conformation, PrPC, or in multiple misfolded pathogenic conformations, collectively called PrPSc. PrPSc is considered infectious because it can recruit and convert its normal isomer PrPC to its pathogenic conformation. This ‘‘protein-only’ ’ concept of infectivity has gained general acceptance and has been extended to explain some unusual non-Mendelian genetic elements in the budding yeast Saccharomyces cerevisiae. In yeast, these factorsare transmitted from mother to daughter cell as particular self-propagating protein conformations, and are thus referred to as yeast prions [2]. Yeast prions share many features with PrPSc: both are capabl