Characterization of Sup35, Rnq1, and Ure2 Cotranslational Prion Aggregation in Saccharomyces cerevisiae

Prions are a unique class of self‐propagating proteins that can adopt self‐propagating misfolded conformations and which can spread through templated self‐conversion. In mammals, prions are unerringly deadly elements of disease, underlying the fatal transmissible spongiform encephalopathies. In yeast, however, prions may actually serve to benefit the cell under various stress conditions, and have been shown to confer a fitness advantage in diverse extracellular environments. Prions are thought to originate de novo from a single misfolding event that could potentially occur either cotranslationally on the ribosome or post‐translationally in the cytosol. While post‐translational prion formation is known to occur, cotranslational prion formation has not yet been conclusively demonstrated. To test whether prions can form cotranslationally, we have constructed plasmids encoding Sup35, Rnq1, and Ure2 prion proteins containing an internal hemagglutinin epitope tag and confirmed their expression in yeast. Using these tools, we tested for the association of prion‐forming proteins with ribosomes and assessed their aggregation state on the ribosome. Previous work from our laboratory has demonstrated that the ribosome‐associated complex (RAC), which protects nascent chains from misfolding, antagonizes prion formation. Thus, the potential exists for regulation of co‐translational prion formation in response to environmental stress conditions. Support or Funding Information National Institute of General Medical Sciences of the National Institutes of Health Award Number R15GM119081