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Antagonistic interactions between yeast chaperones Hsp104 and Hsp70 in prion curing.

The maintenance of [PSI], a prion-like form of the yeast release factor Sup35, requires a specific concentration of the chaperone protein Hsp104: either deletion or overexpression of Hsp104 will cure cells of [PSI]. A major puzzle of these studies was that overexpression of Hsp104 alone, from a heterologous promoter, cures cells of [PSI] very efficiently, yet the natural induction of Hsp104 with heat shock, stationary-phase growth, or sporulation does not. These observations pointed to a mechanism for protecting the genetic information carried by the [PSI] element from vicissitudes of the environment. Here, we show that simultaneous overexpression of Ssa1, a protein of the Hsp70 family, protects [PSI] from curing by overexpression of Hsp104. Ssa1 protein belongs to the Ssa subfamily, members of which are normally induced with Hsp104 during heat shock, stationary-phase growth, and sporulation. At the molecular level, excess Ssa1 prevents a shift of Sup35 protein from the insoluble (prion) to the soluble (cellular) state in the presence of excess Hsp104. Overexpression of Ssa1 also increases nonsense suppression by [PSI] when Hsp104 is expressed at its normal level. In contrast, hsp104 deletion strains lose [PSI] even in the presence of overproduced Ssa1. Overproduction of the unrelated chaperone protein Hsp82 (Hsp90) neither cured [PSI] nor antagonized the [PSI]-curing effect of overproduced Hsp104. Our results suggest it is the interplay between Hsp104 and Hsp70 that allows the maintenance of [PSI] under natural growth conditions.

Pubmed ID: 9891066


  • Newnam GP
  • Wegrzyn RD
  • Lindquist SL
  • Chernoff YO


Molecular and cellular biology

Publication Data

February 12, 1999

Associated Grants

  • Agency: NIGMS NIH HHS, Id: 1R21GM55091

Mesh Terms

  • Adenosine Triphosphatases
  • Fungal Proteins
  • Gene Expression
  • Genes, Fungal
  • HSP70 Heat-Shock Proteins
  • HSP90 Heat-Shock Proteins
  • Heat-Shock Proteins
  • Prions
  • Protein Conformation
  • Saccharomyces cerevisiae
  • Saccharomyces cerevisiae Proteins
  • Solubility
  • Suppression, Genetic
  • Temperature