Prion strains can be distinguished by differences in incubation times, distribution of spongiform pathology, and the pattern of PrPSc deposition. For many years the existence of prion strains. For many years the existence of prion strains was used as an argument for the existence of an essential, as yet unidentified, nucleic acid in the prion particle. During the past five years, considerable evidence has accumulated arguing that the properties of prion strains are enciphered in the conformation of PrPSc. Using a conformation-dependent immunoassay (CDI), we detected differences in the tertiary structures of PrPSc for either different strains. Moreover, the levels of protease-sensitive PrPSc were found to correlate with the length of the strain specified incubation time. We plan to purify both protease-sensitive and-resistant PrPSc from the brains of Syrian hamsters infected with different prion strains and to compare the physical and biological properties of these PrP isoforms. Whether protease- sensitive PrPSc carries prion infectivity of whether it can be converted into protease resistant PrPSc remains to be established. Since studies of protease-sensitive PrPSc support the proposal that PrPSc clearance may determine the length of the incubation time, we plan to determine the rates of formation and clearance for both protease-sensitive and -resistant PrPSc. To do this, bigenic mice expressing tetracycline-regulated PrP transgenes that are inoculated with different strains will be studied. To assess the relative roles of conformation and glycosylation in the enciphering of strain specified properties, we propose to construct transgenic mice expressing glycosylation in the enciphering of strain specified properties, we propose to construct transgenic mice expressing glycosylation deficient PrPs and determine if they are competent for replication of different prion strains. With Gln substitutions at Asn-linked initiated the formation of unglycosylated PrPSc. In this proposal, we introduce the concept that prion strain variation might arise from two sources: (1) qualitative differences in conformation of PrPSc or (2) quantitative variations in the ratio of discrete conformers. In some cases, strains with similar biological characteristics may be distinguished primarily by variations in the ratio of conformers. In other cases, particularly where mor extreme phenotypic differences are observed, distinct conformers of PrPSc may be identified.
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