Introduction to Yeast and Fungal Prions

“Prion” now means “infectious protein, " not requiring an accompanying nucleic acid for transmission to a new individual. In 1994, we found that the long-known cytoplasmic genes [URE3] and [PSI+] were actually prions of Ure2p and Sup35p, respectively. These, and a variety of yeast and fungal prions found since then, are based on self-propagating amyloids, but one prion based on a self-activating protease showed that not all infectious proteins are amyloids. The importance of chaperones and other cellular components in prion propagation and generation, including the discovery of cellular anti-prion systems-some with homologs or at least analogs in mammals, have enriched the prion field. The folded in-register parallel architecture of yeast prion amyloids can explain how a single protein can faithfully propagate any of several structurally different prion variants/strains. Prion variants/strains based on phenotype intensity, propagation stability, sensitivity to anti-prion systems, propagon number, pathogenicity, and other properties have been recognized.