Effects of ubiquitin system on formation and maintenance of a yeast prion.
Tatiana A. Chernova (1), Kim D. Allen (2), E. Paula Tennant (2), Keith D. Wilkinson (1), Yury O. Chernoff (2)
(1) Department of Biochemistry, Emory University, 1510 Clifton Rd., Atlanta, GA, 30322, USA;
(2) School of Biology and IBB, Georgia Institute of Technology, 310 Ferst Drive, Atlanta, GA, 30332, USA
Although proteasome inhibitors affect the turnover of mammalian prion proteins, and ubiquitin (Ub) is associated with some amyloid aggregates, the role of Ub proteolysis in prion formation is not defined. We used [PSI+], a prion isoform of the yeast translation termination factor Sup35, as a model to identify the components of Ub system involved in prion formation and propagation. Deletions of genes encoding deubiquitinating enzymes, critical for Ub regeneration at the proteasome (Ubp6) or the vacuole (Doa4), cause pleiotropic phenotypic effects that are primarily due to decreased levels of free Ub in the yeast cells. These alterations as well as deletion of the gene encoding one of the major Ub-conjugating enzyme, Ubc4, decreased [PSI+] curing by overproduced disaggregase Hsp104, suggesting that Ub system influences Hsp104-dependent clearance of prion aggregates. Spontaneous [PSI+] formation was increased in the ubc4∆ cells, while [PSI+] induction by Sup35 overproduction remained unaffected by ubc4∆, was decreased in the ubp6∆ and doa4∆ cells, and increased by Ub overproduction. Thus, effects of the Ub system on [PSI+] formation depend on Sup35 levels in the yeast cell. The ability of the yeast cells to ubiquitinate Sup35 and another prion protein, Rnq1, known to influence [PSI+] formation, is being investigated. A model explaining the effects of the Ub system on [PSI+] is presented.
Return to YGM 2004 Home at SGD