Evidence for an essential DNA component in the Scrapie agent

Abstract

ONE of the enigmas of microbiology has been the nature of the aetiological agent causing scrapie disease in sheep and goats. The unusual resistance of infectivity to heat, formaldehyde, nucleases and UV irradiation has stimulated many hypotheses, including speculation that the scrapie agent may lack nucleic acid¹. This stability to physical and chemical inactivation has been due in part to the intimate association of the agent with the cell membrane^2,3, making it impossible to obtain soluble fractions of brain tissue containing high titres of infectivity. A hamster model of scrapie disease has been developed^4,5 that has shorter incubation periods and higher brain titres of infectivity than any other animal model. Studies on the subcellular distribution of scrapie agent in hamster brain have shown that 8–9% of the total infectivity can be found in membrane-free high-speed supernatant (HSS) fractions⁶. Infectivity in the HSS exists as small heterogeneous complexes which are resistant to detectable enzymatic degradation, but are more sensitive to inactivation by heat and UV irradiation than are cruder brain preparations⁷. We report here further partitioning of scrapie infectivity in the HSS using two methods of separation, hydroxyapatite chromatography and polyacrylamide gel electrophoresis, both of which result in isolation of a fraction of scrapie infectivity that is inactivated by deoxyribonuclease (DNase). We therefore conclude that the scrapie agent contains an essential DNA component.