Heritable yeast prions have a highly organized three-dimensional architecture with interfiber structures.

Area of Science:

• Cell Biology
• Molecular Biology
• Structural Biology

Background:

• Yeast prions, such as [PSI(+)], are protein-only inheritance elements that alter phenotypes through conformational changes of proteins like Sup35.
• The cellular architecture governing prion inheritance, beyond the amyloid fibril, remains largely unknown.
• Understanding prion assembly is crucial for deciphering their role in phenotypic diversity.

Purpose of the Study:

• To investigate the 3D arrangement of yeast [PSI(+)] prions within their cellular context in a native, hydrated state.
• To elucidate the cellular architecture underlying prion-based inheritance.
• To identify potential self-organizing mechanisms coordinating prion assembly and inheritance.

Main Methods:

• Utilized cryosectioning of vitrified yeast cells.
• Employed cryo-electron tomography to visualize prion assemblies in situ.
• Applied subtomogram image averaging to analyze the organized fibril arrays.

Main Results:

• Identified yeast [PSI(+)] prions as aligned bundles of regularly spaced amyloid fibrils in the cytoplasm.
• Observed that these fibril arrays are not membrane-bound but exclude other cellular components like ribosomes.
• Discovered an additional array of densities between the fibrils, suggesting a structural organizing principle.

Conclusions:

• The study reveals the in situ 3D structure of yeast prions, showing them as organized fibril arrays.
• The observed inter-fibril densities suggest a self-organizing mechanism involved in prion fiber deposition and inheritance regulation.
• This provides new insights into the cellular architecture supporting protein-based inheritance in yeast.