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Evolutionary conservation of prion-forming abilities of the yeast Sup35 protein
Y O Chernoff1, A P Galkin, E Lewitin
1School of Biology, Georgia Institute of Technology, Atlanta, GA 30332-0230, USA.
Abstract:
Saccharomyces cerevisiae prion [PSI ] is a self-propagating isoform of the eukaryotic release factor eRF3 (Sup35p). Sup35p consists of the evolutionary conserved release factor domain (Sup35C) and two evolutionary variable regions - Sup35N, which serves as a prion-forming domain in S. cerevisiae, and Sup35M. Here, we demonstrate that the prion form of Sup35p is not observed among industrial and natural strains of yeast. Moreover, the prion ([PSI + ]) state of the endogenous S. cerevisiae Sup35p cannot be transmitted to the next generations via heterologous Sup35p or Sup35NM, originating from the distantly related yeast species Pichia methanolica. This suggests the existence of a 'species barrier' in yeast prion conversion. However, the chimeric Sup35p, containing the Sup35NM region of Pichia, can be turned into a prion in S. cerevisiae by overproduction of the identical Pichia Sup35NM. Therefore, the prion-forming potential of Sup35NM is conserved in evolution. In the heterologous system, overproduction of Pichia Sup35p or Sup35NM induced formation of the prion form of S. cerevisiae Sup35p, albeit less efficiently than overproduction of the endogenous Sup35p. This implies that prion induction by protein overproduction does not require strict correspondence of the 'inducer' and 'inducee' sequences, and can overcome the 'species barrier'.
Insights
The Saccharomyces cerevisiae prion [PSI+] is not found in natural yeast strains. However, protein overproduction can overcome species barriers, enabling prion formation across different yeast species.
Area of Science:
- Molecular Biology
- Yeast Genetics
- Prion Biology
Background:
- The [PSI+] prion in Saccharomyces cerevisiae is a self-propagating isoform of the eukaryotic release factor eRF3 (Sup35p).
- Sup35p comprises a conserved release factor domain (Sup35C) and variable regions, including the prion-forming Sup35N domain and Sup35M.
- Understanding prion propagation and interspecies transmission is crucial for prion biology.
Purpose of the Study:
- To investigate the presence of the [PSI+] prion in natural and industrial yeast strains.
- To determine if the [PSI+] state can be transmitted between Saccharomyces cerevisiae and Pichia methanolica.
- To explore the role of Sup35N and Sup35NM in interspecies prion conversion and the potential for overcoming species barriers.
Main Methods:
- Analysis of prion formation in industrial and natural yeast strains.
- Heterologous expression experiments involving Sup35p and Sup35NM from S. cerevisiae and P. methanolica.
- Induction of prion formation via protein overproduction in interspecies systems.
Main Results:
- The [PSI+] prion was not observed in natural or industrial yeast strains.
- Endogenous S. cerevisiae Sup35p prion state was not transmitted to P. methanolica Sup35p or Sup35NM, indicating a species barrier.
- Chimeric Sup35p (with Pichia Sup35NM) could form prions in S. cerevisiae upon Pichia Sup35NM overproduction, demonstrating conserved prion-forming potential.
- Overproduction of Pichia Sup35p or Sup35NM induced S. cerevisiae Sup35p prion formation, albeit less efficiently, suggesting sequence similarity is not strictly required for induction.
Conclusions:
- A species barrier exists for yeast prion conversion between S. cerevisiae and P. methanolica.
- The prion-forming domain Sup35NM exhibits conserved evolutionary potential.
- Protein overproduction can overcome species barriers in prion induction, even without strict sequence homology.