Differences between the five antibodies used. Blots showing six bovine C-type BSE samples (a to f) analysed by five antibodies. Two molecular marker kits are each applied twice (lanes 1, 5, 9, and 10; arrow heads indicate for M1: positions of 20 and 25 kDa; and for M2: 20, 30 and 40 kDa). The groups to which the antibodies belong are shown at the right and have been defined in . Group A antibodies recognise a region of the protein close to the N-terminus, group B recognises the core of the protein while group C antibodies bind in the C-terminal region of PrP. Antibody concentrations were 2, 0.5, 2 and 0.5 μg/ml for 12B2, 9A2, SAF84 and 94B4 respectively, and for Sha31 the manufacturer's instructions were followed. SDS-PAGE gels were 15%, except for Sha31, which was 13.5%. Tissue equivalents applied were 7.1 mg of fresh brain per lane. The strongly positive BSE cases (e.g. samples a and d) can present an additional light grey band below the unglycosylated PrPres band. This corresponds to an unidentified PrP fragment.