Regulated Prion Formation

Abstract

Prions are infectious proteins responsible for tranmissible spongiform encephalopathies in mammals including humans. Two yeast prions have been identified [URE3] and [PSI+], which are prion forms of Ure2p and Sup35p, respectively. Edskes and Wickner designed experiments based on the fact that [URE3] would cause uptake of ureidosuccinate (USA) in the presence of ammonia to identify pathways involved in the de novo production of this prion. USA uptake in the presence of ammonia was severely inhibited by deletion of MKS1 and its protein, which is inhibited by the Ras-regulated cyclic adenosine monophosphate (cAMP) pathway that inhibits Ure2p in the absence of a good nitrogen source. Furthermore, a constitutively active RAS allele was able to also promote USA uptake in the presence of ammonia. These results suggest that Mks1p and the Ras-cAMP pathway can regulate de novo prion formation. However, deletion of MKS1 did not inhibit propagation of [URE3] introduced by cytoduction implying that the de novo production of prions and the propagation of prions are regulated separately. Edskes, H.K., and Wickner, R.B. (2000) A protein required for prion generation: [URE3] induction requires the Ras-regulated Mks1 protein. Proc. Natl. Acad. Sci. U.S.A. 97 : 6625-6629. [Abstract] [Full Text]