Variant-specific [PSI+] infection is transmitted by Sup35 polymers within [PSI+] aggregates with heterogeneous protein composition

Mol Biol Cell. 2008 Jun;19(6):2433-43. doi: 10.1091/mbc.e08-01-0078. Epub 2008 Mar 19.

Abstract

The [PSI(+)] prion is the aggregated self-propagating form of the Sup35 protein from the yeast Saccharomyces cerevisiae. Aggregates of Sup35 in [PSI(+)] cells exist in different heritable conformations, called "variants," and they are composed of detergent-resistant Sup35 polymers, which may be closely associated with themselves, other proteins, or both. Here, we report that disassembly of the aggregates into individual Sup35 polymers and non-Sup35 components increases their infectivity while retaining their variant specificity, showing that variant-specific [PSI(+)] infection can be transmitted by Sup35 polymers alone. Morphological analysis revealed that Sup35 isolated from [PSI(+)] yeast has the appearance of short barrels, and bundles, which seem to be composed of barrels. We show that the major components of two different variants of [PSI(+)] are interacting infectious Sup35 polymers and Ssa1/2. Using a candidate approach, we detected Hsp104, Ssb1/2, Sis1, Sse1, Ydj1, and Sla2 among minor components of the aggregates. We demonstrate that Ssa1/2 efficiently binds to the prion domain of Sup35 in [PSI(+)] cells, but that it interacts poorly with the nonaggregated Sup35 found in [psi(-)] cells. Hsp104, Sis1, and Sse1 interact preferentially with the prion versus nonprion form of Sup35, whereas Sla2 and Ssb1/2 interact with both forms of Sup35 with similar efficiency.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Immunoblotting
  • Peptide Termination Factors
  • Polymers / chemistry*
  • Polymers / metabolism*
  • Prions / chemistry*
  • Prions / metabolism*
  • Prions / ultrastructure
  • Protein Binding
  • Protein Structure, Quaternary
  • Saccharomyces cerevisiae / drug effects
  • Saccharomyces cerevisiae / metabolism*
  • Saccharomyces cerevisiae / ultrastructure
  • Saccharomyces cerevisiae Proteins / chemistry
  • Saccharomyces cerevisiae Proteins / metabolism*
  • Saccharomyces cerevisiae Proteins / ultrastructure
  • Sodium Dodecyl Sulfate / pharmacology

Substances

  • Peptide Termination Factors
  • Polymers
  • Prions
  • SUP35 protein, S cerevisiae
  • Saccharomyces cerevisiae Proteins
  • Sodium Dodecyl Sulfate