Prion Propagation in Response to Temperature and Osmotic Stress Jess Dhillon Department of Biological Sciences, York College of Pennsylvania Introduction First hypothesized in the late 1960’s, prions cause several neurodegenerative diseases in mammals such as bovine spongiform encephalopathy in cattle and Creutzfeldt–Jakob disease in humans. Stanley Prusiner coined the term prion and received the Nobel Prize in 1997 for his work in prion research. There has been only one prion protein identified in mammals, titled PrP, with a superscript of “c” for common or cellular denoting the normal conformation and Sc for Scrapie denoting the misfolded conformation and one of the diseases originally linked to prions (Colby et al 2007). In yeast, Saccharomyces cerevisiae, a translational termination factor Sup35p can propagate as a prion called [PSI + ] (Tank et al 2007). This is the model we used since yeast prions are noninfectious in mammals and previous research has shown that PrP can replace Sup35p in yeast and retain the prion competence indicating that they may structurally mimic each other (Parham et al 2001). Objectives  Verify yeast strains using dropout plates  Determine the effects of temperature and osmotic stress on the molecular chaperones Ssa1, Ssb1, and Ssb2 Methods Results  Heat shock induced a strong phenotypic switch from [PSI + ] to [PSI - ] in the ssa1 and a weak one the ssb2 deletion strains  Osmotic shock induced a strong phenotypic switch from [PSI + ] to [PSI - ] in the ssa1 and a weak one in the ssb1 and ssb2 deletion strains Figure 2. Parent [PSI + ] strain showing no phenotypic switch after osmotic shock Figure 3. ssa1Δ [PSI + ] strain showing a strong phenotypic switch after osmotic shock Firgure 4. ssb2Δ [PSI + ] strain showing a weak phenotypic switch after heat shock Discussion The ability of the molecular chaperones Ssa1p, Ssb1p, and Ssb2p to help in the folding of the Sup35 protein following heat and osmotic shock is hindered. This research indicates that certain types of cellular stress are capable of affecting a prions ability to maintain its conformation and could possible lead to novel approaches for treating prion diseases in mammals. Instead of attempting to remove the prions from the affected mammal it is conceivable that inducing a stressor when hindering a molecular chaperone can lead to the folding of the non-infectious conformation instead. Literature cited Colby, David W. et al. Protease-Sensitive Synthetic Prions. PLoS Pathogens; Jan2010, Vol. 7 Issue 1, p1-9 Nakayashiki, Toru et al. Yeast [PSI + ] “Prions” that Are Crosstransmissible and Susceptible beyond a Species Barrier through a Quasi-Prion State. Molceular Cell, Volume 7, Issue 6, June 2001, Pages Tank, Elizabeth M. H. et al. Prion Protein Repeat Expansion Results in Increased Aggrgation and Reveals Phenotypic Variability. Molecular and Cellular Biology. August 2007 p Acknowledgements Dr. David Singleton, Research Mentor York College Biology Department Abstract Prions are misfolded proteins that have been shown to cause neurodegenerative disease in mammals. To determine the affects of molecular chaperones on the folding of prions, strains of yeast with specific gene deletions for molecular chaperones were stress induced and using red-white sectoring were monitored for prion conformation. Phenotypic variation was seen in several strains following heat or osmotic shock. Conclusion The refolding of the prion Sup35 in yeast in strains with gene deletions for specific molecular chaperones is shown to cause phenotypic variation following heat or osmotic shock Fig. 2 Fig. 3 Fig. 4 Figure 1. Using the ade 1-14 readout, the colonies appear phenotypically red with functioning chaperones or white with chaperone gene deletions and shock