MOLECULAR MECHANISMS OF PROTEIN HEREDITY - YEAST PRIONS

Here we summarize data on prions, proteinaceous infectious agents caus ing incurable degenerative neurologic diseases in mammals. Evidence is presented that the genetic properties of the nonchromosomally inherit ed determinants [URE3] and [PSI+] of the yeast Saccharomyces cerevisia e are associated with prion-like behavior of the proteins Ure2p and Su p35p, respectively. Sup35p from the [PSI+] cells is shown to differ by a number of physicochemical characteristics from the same protein iso lated from cells lacking this determinant but be similar to the pathog enic form of the mammalian prion PrP. When applied to yeast, the prion concept allows one to propose a new mechanism of epigenetic ''protein '' inheritance of traits and to hypothesize that the conversion of nor mal Ure2p and Sup35p into the prion-like form represents an example of a mechanism by which gene activity is regulated at a posttranslationa l level.