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Molecular and Cellular Biology, June 2002, p. 3590-3598, Vol. 22, No. 11
0270-7306/02/$04.00+0     DOI: 10.1128/MCB.22.11.3590-3598.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Antagonistic Interactions between Yeast [PSI+] and [URE3] Prions and Curing of [URE3] by Hsp70 Protein Chaperone Ssa1p but Not by Ssa2p

Christine Schwimmer and Daniel C. Masison*

Laboratory of Biochemistry and Genetics, National Institute of Diabetes, Digestive, and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0851

Received 10 September 2001/ Returned for modification 24 October 2001/ Accepted 21 February 2002

The yeast [PSI+], [URE3], and [PIN+] genetic elements are prion forms of Sup35p, Ure2p, and Rnq1p, respectively. Overexpression of Sup35p, Ure2p, or Rnq1p leads to increased de novo appearance of [PSI+], [URE3], and [PIN+], respectively. This inducible appearance of [PSI+] was shown to be dependent on the presence of [PIN+] or [URE3] or overexpression of other yeast proteins that have stretches of polar residues similar to the prion-determining domains of the known prion proteins. In a similar manner, [PSI+] and [URE3] facilitate the appearance of [PIN+]. In contrast to these positive interactions, here we find that in the presence of [PIN+], [PSI+] and [URE3] repressed each other's propagation and de novo appearance. Elevated expression of Hsp104 and Hsp70 (Ssa2p) had little effect on these interactions, ruling out competition between the two prions for limiting amounts of these protein chaperones. In contrast, we find that constitutive overexpression of SSA1 but not SSA2 cured cells of [URE3], uncovering a specific interaction between Ssa1p and [URE3] and a functional distinction between these nearly identical Hsp70 isoforms. We also find that Hsp104 abundance, which critically affects [PSI+] propagation, is elevated when [URE3] is present. Our results are consistent with the notion that proteins that have a propensity to form prions may interact with heterologous prions but, as we now show, in a negative manner. Our data also suggest that differences in how [PSI+] and [URE3] interact with Hsp104 and Hsp70 may contribute to their antagonistic interactions.

* Corresponding author. Mailing address: Building 8, Room 407, Laboratory of Biochemistry and Genetics, National Institute of Diabetes, Digestive, and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0851. Phone: (301) 594-1316. Fax: (301) 496-9431. E-mail: masisond{at}helix.nih.gov.

Molecular and Cellular Biology, June 2002, p. 3590-3598, Vol. 22, No. 11
0022-538X/02/$04.00+0     DOI: 10.1128/MCB.22.11.3590-3598.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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