Fig. 1.

Strain-specific sequences of [PSI]. (A) Proline substitutions. (B) Glycine insertions (in every other amino acid position, Gi5 indicates insertion of a glycine residue before residue 5 of the native sequence). [PSI] strains are labeled on the left. The compatibilities of Sup35 single mutations (labeled on bottom) are judged by nonsense read-through of the ade2–1(UAA) allele (1 = WT nonsense suppression efficiency, indicating efficient prion propagation; 0 = no suppression, indicating loss of prion). Red enclosing rectangles indicate prion loss in pro/WT or Gi/WT heterozygotes. Black bars at [VH] R28P and [VH] Gi47 indicate two populations of the mutant colonies exist, one with reduced nonsense suppression (0.5). [PSI] strain types remain unchanged in all mutations with altered (≠ 1, 0) nonsense suppression. Continuous sequence segments consisting of incompatible mutants are underlined with green (A) and yellow bars (B), respectively.