Table 2.

Arguments for prions being composed largely, if not entirely, of PrP^Sc molecules and devoid of nucleic acid

1	PrPSc and scrapie infectivity copurify when biochemical and immunologic procedures are used.
2	The unusual properties of PrPSc mimic those of prions. Many different procedures that modify or hydrolyze PrPSc inactivate prions.
3	Levels of PrPSc are directly proportional to prion titers. Nondenatured PrPSc has not been separated from scrapie infectivity.
4	No evidence exists for a virus-like particle or a nucleic acid genome.
5	Accumulation of PrPSc is invariably associated with the pathology of prion diseases, including PrP amyloid plaques that are pathognomonic.
6	PrP gene mutations are genetically linked to inherited prion disease and cause formation of PrPSc.
7	Overexpression of PrPC increases the rate of PrPSc formation, which shortens the incubation time. Knock out of the PrP gene eliminates the substrate necessary for PrPSc formation and prevents both prion disease and prion replication.
8	Species variations in the PrP sequence are responsible, at least in part, for the species barrier that is found when prions are passaged from one host to another.
9	PrPSc preferentially binds to homologous PrPC, resulting in formation of nascent PrPSc and prion infectivity.
10	Chimeric and partially deleted PrP genes change susceptibility to prions from different species and support production of artificial prions with novel properties that are not found in nature.
11	Prion diversity is enciphered within the conformation of PrPSc. Strains can be generated by passage through hosts with different PrP genes. Prion strains are maintained by PrPC/PrPSc interactions.
12	Human prions from fCJD(E200K) and FFI patients impart different properties to chimeric MHu2M PrP in transgenic mice, which provides a mechanism for strain propagation.