title: Hsp70/Hsp90 co-chaperones are required for efficient Hsp104-mediated elimination of the yeast [PSI(+)] prion but not for prion propagation.
abstract: The continued propagation of the yeast [PSI(+)] prion requires the molecular chaperone Hsp104 yet in cells engineered to overexpress Hsp104; prion propagation is impaired leading to the rapid appearance of prion-free [psi(-)] cells. The underlying mechanism of prion loss in such cells is unknown but is assumed to be due to the complete dissolution of the prion aggregates by the ATP-dependent disaggregase activity of this chaperone. To further explore the mechanism, we have sought to identify cellular factors required for prion loss in such cells. Sti1p and Cpr7p are co-chaperones that modulate the activity of Hsp70/Ssa and Hsp90 chaperones and bind to the C-terminus of Hsp104. Neither Sti1p nor Cpr7p is necessary for prion propagation but we show that deletion of the STI1 and CPR7 genes leads to a significant reduction in the generation of [psi(-)] cells by Hsp104 overexpression. Deletion of the STI1 and CPR7 genes does not modify the elimination of [PSI(+)] by guanidine hydrochloride, which inhibits the ATPase activity of Hsp104 but does block elimination of [PSI(+)] by overexpression of either an ATPase-defective mutant of Hsp104 (hsp104(K218T/K620T)) or a 'trap' mutant Hsp104 (hsp104(E285Q/E687Q)) that can bind its substrate but can not release it. These results provide support for the hypothesis that [PSI(+)] elimination by Hsp104 overexpression is not simply a consequence of complete dissolution of the prion aggregates but rather is through a mechanism distinct from the remodelling activity of Hsp104.
authors.affiliation: Kent Fungal Group, School of Biosciences, University of Kent, Canterbury, UK.
authors.forename: Behrooz
authors.initials: B
authors.lastname: Moosavi
authors.forename: Jintana
authors.initials: J
authors.lastname: Wongwigkarn
authors.forename: Mick F
authors.initials: MF
authors.lastname: Tuite
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics; D000081406:Peptidyl-Prolyl Isomerase F; D021983:Cyclophilins / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D018841:HSP90 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D020125:Mutation, Missense; D011328:Prions / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D000097322:Peptidyl-Prolyl Isomerase D
chemical_list: D000081406:Peptidyl-Prolyl Isomerase F; D021983:Cyclophilins; D018840:HSP70 Heat-Shock Proteins; D018841:HSP90 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D050505:Mutant Proteins; D011328:Prions; D029701:Saccharomyces cerevisiae Proteins; C000631445:CPR7 protein, S cerevisiae; D000097322:Peptidyl-Prolyl Isomerase D; C074510:HSP82 protein, S cerevisiae; C090869:SSA3 protein, S cerevisiae; C542289:STI1 protein, S cerevisiae; C070972:HsP104 protein, S cerevisiae