“…By mixing together PrP Sc and recPrP expressed in mammalian cell lines to result in newly protease resistant PrP (PrP Res ) the group of Byron Caughey showed that PrP Sc can auto-catalytically seed the conformational conversion of recPrP (Kocisko et al, 1994). This technique was termed the cell free conversion assay (CFCA) and it was subsequently shown to mimic many aspects of disease seen in vivo, including species barriers (Kirby et al, 2003, Kocisko et al, 1995 and the inhibitory effects of specific chemicals , Demaimay et al, 2000, Demaimay et al, 1998. Quantifying conversion efficiency allows insights into mechanistic aspects of conversion: for example, there are two distinct phases of prion protein conversion -binding followed by conformational alteration (Horiuchi & Caughey, 1999) -and single amino acid substitutions were shown to dramatically affect the efficiency of conversion of the substrate (Bossers et al, 1997, Eiden et al, 2011, Kirby et al, 2006.…”