Comparison of sequence variants in the PrP GPI-SP region. Precursor PrP structural features include: an N-terminus signal peptide (N-SP), a five octapeptide repeat region (5-OR), a hydrophobic region (H), a disulfide bridge (S-S), N-linked glycosylation sites (dots), and a GPI signal peptide (GPI-SP). The residue numbers above the consensus sequence are those for ovine PrP. The peptide cleavage and GPI attachment site is indicated by omega-site zero (ω0). After synthesis and translocation to the endoplasmic reticulum, a GPI moiety is typically attached to the ω0 site of wild-type precursor PrP by a transamidation reaction and the last 23 residues are cleaved. The residues associated with familial CJD are shown in bold (M232R [34–37], M232T , P238S ). For comparison, nonsynonymous substitutions encoded by ovine PRNP are also shown in bold (L237P, this work; P241S [21, 57]).