The sensitive [SWI (+)] prion: new perspectives on yeast prion diversity.

Yeast prions are heritable protein-based genetic elements which rely on molecular chaperone proteins for stable transmission to cell progeny. Within the past few years, five new prions have been validated and 18 additional putative prions identified in Saccharomyces cerevisiae. The exploration of the physical and biological properties of these "nouveau prions" has begun to reveal the extent of prion diversity in yeast. We recently reported that one such prion, [SWI(+)], differs from the best studied, archetypal prion [PSI(+)] in several significant ways. ( 1) Notably, [SWI(+)] is highly sensitive to alterations in Hsp70 system chaperone activity and is lost upon growth at elevated temperatures. In that report we briefly noted a correlation amongst prions regarding amino acid composition, seed number and sensitivity to the activity of the Hsp70 chaperone system. Here we extend that analysis and put forth the idea that [SWI(+)] may be representative of a class of asparagine-rich yeast prions which also includes [URE3], [MOT3(+)] and [ISP(+)], distinct from the glutamine-rich prions such as [PSI(+)] and [RNQ(+)]. While much work remains, it is apparent that our understanding of the extent of the diversity of prion characteristics is in its infancy.