Infectious scrapie prions are composed largely, if not entirely, of an abnormal isoform of the
prion protein (PrP) which is designated PrPSc. A chromosomal gene encodes both the
cellular prion protein (PrPC) as well as PrPSc. Pulse-chase experiments with scrapie-
infected cultured cells indicate that PrPSc is formed by a post-translational process. PrP is
translated in the endoplasmic reticulum, modified as it passes through the Golgi, and is
transported to the cell surface. Release of nascent PrP from the cell surface by …