Scrapie infectivity, fibrils and low molecular weight protein.

The development of a short incubation model of scrapie (strain 263K), in golden hamsters has added impetus to the purification of the infectious agent. Our own attempts have been based on methods pioneered by Millson and developed by Prusiner. We present here results indicating that a purification factor of up to 10(4) with respect to protein may now be possible. Fractions from brain with high infectivity had a sedimentation range of 70-300S and contained an abundance of fibrils closely similar to the scrapie-associated fibrils (SAF) discovered by Merz et al.. Material of molecular weight (Mr) 26,000, which is probably protein, appears to be a major constituent of the fibrils. The association between infectivity and fibrils raises two possibilities: the fibrils are an infectious form of the scrapie agent or they are a pathological response to scrapie infection.