Self-perpetuating cross-β aggregated proteins (prions) are associated with fatal transmissible spongiform encephalopathies in mammals (including humans) and control heritable traits in yeast and other fungi. Prion diseases, such as sheep scrapie, bovine spongiform encephalopathy (BSE), chronic wasting disease (CWD) and human Creutzfeldt-Jakob disease, are transmitted by the prion protein (PrP) that converts normal cellular protein of the same sequence into a polymeric cross-β (prion) isoform. Prion transmission depends on the identity of interacting amino acid sequences, so that the transmission barriers are observed between divergent species. However, these barriers can be overcome. For example, BSE transmission to humans is a huge problem for the cattle industry and for a public health. The mechanisms of cross-species prion transmission are still poorly understood. We used a yeast Sup35/[PSI+] model to explore the molecular basis of prion transmission barriers. In contrast to the previous experimental setti