UASt drives expression of the mature Mmus\Prnp 3F4 protein (the 3F4 epitope is created via two amino acid substitutions, L108M and V111M, and is already present in wild-type human and hamster PrP) carrying a single-codon mutation (D177N) associated with fatal familial insomnia (FFI) prion disease in humans, flanked by the coding sequence of its autologous leader peptide and GPI signal sequence.