A novel, resistance-linked ovine PrP variant and its equivalent mouse variant modulate the in vitro cell-free conversion of rPrP to PrPres

1 Institute for Animal Health, Compton Laboratories, Newbury, Berkshire RG20 7NN, UK 2 Neuropathogenesis Unit, Institute for Animal Health, Ogston Building, West Mains Road, Edinburgh EH9 3JF, UK Correspondence Louise Kirby louise.kirby{at}bbsrc.ac.uk Prion diseases are associated with the conversion of the normal cellular prion protein, PrP c , to the abnormal, disease-associated form, PrP Sc . This conversion can be mimicked in vitro by using a cell-free conversion assay. It has recently been shown that this assay can be modified to use bacterial recombinant PrP as substrate and mimic the in vivo transmission characteristics of rodent scrapie. Here, it is demonstrated that the assay replicates the ovine polymorphism barriers of scrapie transmission. In addition, the recently identified ovine PrP variant ARL 168 Q, which is associated with resistance of sheep to experimental BSE, modulates the cell-free conversion of ovine recombinant PrP to PrP res by three different types of PrP Sc , reducing conversion efficiencies to levels similar to those of the ovine resistance-associated ARR variant. Also, the equivalent variant in mice (L 164 ) is resistant to conversion by 87V scrapie. Together, these results suggest a significant role for this position and/or amino acid in conversion.