TSEs are a group of neurodegenerative diseases affecting a wide variety of mammals including sheep and goats (scrapie), cervid spp. (chronic wasting disease), and humans (Creutzfeldt-Jakob disease). Our studies are focused on the prion protein (PrP) due to the critical role of this protein in controlling many aspects of TSE pathogenesis such as susceptibility to disease and interspecies transmission. A central event in TSE disease involves the conversion of the normal host cellular prion protein (PrPC or PrP-sen) to a partially protease-resistant, aggregated, disease-associated isoform (PrPSc or PrP-res). TSE-induced pathology is usually associated with PrP-res deposition, but the mechanism of neurodegeneration is not understood.<P> The nature of the infectious agent, called a prion, remains uncertain but is thought to be composed primarily of misfolded PrP, perhaps in complex with another host accessory molecule(s). PrP-sen is a glycosylphosphatidylinositol (GPI)-anchored glycoprotein, and the majority of PrP-res produced in vivo contains this GPI anchor. Membrane association of both normal and disease-associated PrP isoforms may influence many features of prion disease and PrP-sen function.<P>Our work is focused on elucidating mechanisms of uptake, replication, and spread of prions, in addition to determining the biochemical composition of mammalian prions and investigating factors that contribute to imparting the infectious phenotype to these prions, a unique feature among all protein misfolding diseases. <P>Over the past year we have: 1) continued our characterization of a new cell culture model for infection with mouse-adapted scrapie; 2) characterized the effect of PrP-res membrane association on infection of this new cell culture model; 3) attempted to generate prion infectivity in preparations of recombinant PrP assayed in new PrP transgenic mouse models; 4) continued to characterize how PrP-res is internalized and trafficked in neuronal cells by confocal microscopy; 5) developed new methods to specifically tag PrP-sen molecules to visualize their trafficking in uninfected cells and during the course of scrapie infection; and 6) established cell culture models to visualize the trafficking of other modified prion and amyloid proteins by confocal microscopy.