A 54-kDa normal cellular protein may be the precursor of the scrapie agent protease-resistant protein.

Scrapie is the best understood of the transmissible spongiform encephalopathies. These neurologic disorders include the human diseases kuru and Creutzfeldt-Jakob disease and are caused by pathogens with unique biological and molecular properties. One major protein, protease-resistant protein (PrP)-27-30, is present in fractions isolated from scrapie-infected hamster brain that contain highly purified scrapie agent. PrP-27-30 appears to be the major protein component of the hamster scrapie agent. An antiserum generated to electrophoretically purified hamster scrapie PrP-27-30 identified higher molecular weight proteins in immunoblots of homogenates of uninfected hamster and mouse brains. Antibodies to hamster and mouse scrapie agent proteins were obtained by immunoaffinity purification of this antiserum. These antibodies to hamster and mouse PrPs recognized a 54-kDa protein present in uninfected brain homogenates. Antibodies immunoaffinity purified from this antiserum using whole immunoblots of normal brain antigens also identified the 54-kDa protein and PrPs. Our findings demonstrate that scrapie agent proteins share epitopes with normal proteins and suggest that the 54-kDa protein is the normal protein precursor of the scrapie agent PrPs.