The prions (infectious proteins) of Saccharomyces cerevisiae are proteins acting 
as genes, by templating their conformation from one molecule to another in 
analogy to DNA templating its sequence. Most yeast prions are amyloid forms of 
normally soluble proteins, and a single protein sequence can have any of several 
self-propagating forms (called prion strains or variants), analogous to the 
different possible alleles of a DNA gene. A central issue in prion biology is 
the structural basis of this conformational templating process. The in-register 
parallel β sheet structure found for several infectious yeast prion amyloids 
naturally suggests an explanation for this conformational templating. While most 
prions are plainly diseases, the [Het-s] prion of Podospora anserina may be a 
functional amyloid, with important structural implications. Yeast prions are 
important models for human amyloid diseases in general, particularly because new 
evidence is showing infectious aspects of several human amyloidoses not 
previously classified as prions. We also review studies of the roles of 
chaperones, aggregate-collecting proteins, and other cellular components using 
yeast that have led the way in improving the understanding of similar processes 
that must be operating in many human amyloidoses.