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Updated: Jul 2, 2026
High-throughput Screening for Protein-based Inheritance in S. cerevisiae
Published on: August 8, 2017
Strain-specific sequences required for yeast [PSI+] prion propagation
Hsiang-Yu Chang1, Jia-Yu Lin, Han-Chung Lee
1Institute of Molecular Biology, Academia Sinica, Taipei 11529, Taiwan.
Abstract:
Amyloid polymorphism underlies the prion strain phenomenon where a single protein polypeptide adopts different chain-folding patterns to form self-propagating cross-beta structures. Three strains of the yeast prion [PSI], namely [VH], [VK], and [VL], have been previously characterized and are amyloid conformers of the yeast translation termination factor Sup35. Here we define specific sequences of the Sup35 protein that are necessary for in vivo propagation of each of these prion strains. By sequential substitution of residues 5-55 of Sup35 by proline and insertion of glycine at alternate sites in this segment, specific mutations have been identified that interfere selectively with the propagation of each of the three prion strains in yeast: the [VH] strain requires amino acid residues 7-21; [VK] requires residues 9-37; and [VL] requires residues 5 to at least 52. Minimal polypeptide segments capable of encoding prion conformations were defined by assembly of recombinant Sup35 fragments on purified prion nuclei to form amyloid fibers in vitro, whose infectivity was assayed in yeast. For the [VK] and [VL] strains, the minimal fragments approximately coincide with the strain-specific sequences defined by mutations of the N-terminal portion of the intact Sup35 (1-685); and for the [VH] strain, a longer Sup (1-53) fragment is required. Polymorphic structures of other amyloids might similarly involve different stretches of polypeptides to form cross-beta amyloid cores with distinct molecular recognition surfaces.
Insights
Yeast prion strains ([VH], [VK], [VL]) are distinct Sup35 protein folding patterns. Specific Sup35 protein sequences dictate the in vivo propagation of each prion strain, revealing key regions for amyloid conformation.
Area of Science:
- Biochemistry
- Molecular Biology
- Structural Biology
Background:
- Prion strains arise from protein polymorphism, where a single polypeptide adopts various self-propagating cross-beta structures.
- The yeast prion [PSI] involves amyloid conformers of the Sup35 protein, a translation termination factor.
- Three characterized yeast prion strains are [VH], [VK], and [VL].
Purpose of the Study:
- To identify specific Sup35 protein sequences essential for the in vivo propagation of the [VH], [VK], and [VL] yeast prion strains.
- To define minimal polypeptide segments encoding prion conformations through in vitro assembly and infectivity assays.
Main Methods:
- Introducing mutations (proline substitutions, glycine insertions) in the N-terminal 5-55 residues of Sup35.
- Assaying prion strain propagation in yeast following mutagenesis.
- Assembling recombinant Sup35 fragments on purified prion nuclei to form amyloid fibers in vitro.
- Assaying the infectivity of in vitro assembled amyloid fibers in yeast.
Main Results:
- Mutations selectively interfered with the propagation of specific prion strains: [VH] requires residues 7-21, [VK] requires residues 9-37, and [VL] requires residues 5-52.
- In vitro studies defined minimal polypeptide segments encoding prion conformations.
- For [VK] and [VL], minimal fragments matched mutation-defined sequences; for [VH], a longer fragment (Sup 1-53) was necessary.
Conclusions:
- Specific N-terminal sequences of Sup35 are critical for the in vivo propagation of distinct prion strains.
- Amyloid polymorphism in other proteins may similarly involve varied polypeptide stretches forming distinct cross-beta amyloid cores.
