Yeast Sup35 Prion Structure: Two Types, Four Parts, Many Variants.

The yeast [] prion, formed by the Sup35 (eRF3) protein, has multiple structural variants differing in the strength of nonsense suppressor phenotype. Structure of [] and its variation are characterized poorly. Here, we mapped Sup35 amyloid cores of 26 [] ex vivo prions of different origin using proteinase K digestion and mass spectrometric identification of resistant peptides. In all [] variants the Sup35 amino acid residues 2-32 were fully resistant and the region up to residue 72 was partially resistant. Proteinase K-resistant structures were also found within regions 73-124, 125-153, and 154-221, but their presence differed between [] isolates. Two distinct digestion patterns were observed for region 2-72, which always correlated with the "strong" and "weak" [] nonsense suppressor phenotypes. Also, all [] with a weak pattern were eliminated by multicopy gene and were not toxic when combined with multicopy . [] with a strong pattern showed opposite properties, being resistant to multicopy and lethal with multicopy . Thus, Sup35 prion cores can be composed of up to four elements. [] variants can be divided into two classes reliably distinguishable basing on structure of the first element and the described assays.