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Prions are not uniquely associated with rare fatal neurodegenerative diseases in the animal kingdom; prions are also found in fungi and in particular the yeast Saccharomyces cerevisiae. As with animal prions, fungal prions are proteins able to exist in one or more self-propagating alternative conformations, but show little primary sequence relationship with the mammalian prion protein PrP. Rather, fungal prions represent a relatively diverse collection of proteins that participate in key cellular processes such as transcription and translation. Upon switching to their prion form, these proteins can generate stable, sometimes beneficial, changes in the host cell phenotype. Much has already been learnt about prion structure, and propagation and de novo generation of the prion state through studies in yeast and these findings are reviewed here.

The study of suppressor mutations that affect translational fidelity provides an efficient approach for identifying new components of the translational machinery in eukaryotes. Some of the identified genes controlling fidelity in lower eukaryotes presumably code for ribosomal proteins (Dequard-Chablat et al, 1986; All-Robyn et al, 1990; Hinnebusch and Liebman, 1991) and translation factors (Sandbaken and Culbertson, 1988; Kushnirov et al, 1988; Breining and Piepersberg, 1986). However, functions of the majority of these genes have not been established.