The purpose of this paper was to screen candidate bacterial strains for the production of proteases suitable for application to the degradation of pathogenic forms of prion protein (PrPSc). This paper describes the biochemical characteristics and proteolytic activity of the isolated protease. After screening more than 200 bacterial proteases for keratinolytic activity, we identified a Bacillus stain that produced a protease exhibiting high-degradation activity against a scrapie PrPSc. Sequence analysis indicated that this serine-protease belonged to the Subtilisin family and had optimum pH and temperature ranges of 9-10 and 60-70 degrees C. Western blotting analysis revealed that the protease was also capable of decomposing bovine spongiform encephalopathy-infected brain homogenate. In addition, the protease was demonstrated to degrade dried PrPSc that had become firmly attached to a plastic surface considerably more effectively than proteinase K or PWD-1, a previously reported keratinase. These results indicate that the isolated protease exhibited higher activity for PrPSc degradation compared with other proteases examined. This protease could be used under moderate conditions for the decontamination of precision instruments that are susceptible to PrPSc contamination.