Protein-only inheritance in yeast: something to get [PSI+]-ched about

Recent work suggests that two unrelated phenotypes, [PSI+] and [URE3], in t he yeast Saccharomyces cerevisiae are transmitted by non-covalent changes i n the physical states of their protein determinants, Sup35p and Ure2p, rath er than by changes in the genes that encode these proteins. The mechanism b y which alternative protein states are self-propagating is the key to under standing how proteins function as elements of epigenetic inheritance. Here, we fonts on recent molecular-genetic analysis of the inheritance of the [P SI+] factor of S. cerevisiae. Insights into this process might be extendabl e to a group of mammalian diseases (the amyloidoses), which are also believ ed to be a manifestation of self-perpetuating changes in protein conformati on.