The Ure2, Sup35, and Rnq1 PFDs are biased toward amyloidogenic disorder-promoting residues. (A to C) Relationship between the degree to which an amino acid promotes prion formation and the amino acid's prevalence within yeast PFDs. ln (ORobs) (from Table 2) was plotted versus ln (ORPFD) (as calculated in equation 1) for the prion domain from Ure2 (A), Sup35 (B), or Rnq1 (C). (D to F) Analysis only of the disorder-prone amino acids Lys, Pro, Gly, Arg, Asn, Gln, Ser, Glu, and Asp.