Mapping of antibody epitopes in DRS-1 protein. (A) Lysates of transformed E coli expressing 3 different DRS-1 fragments (aa's 61-74, aa's 144-166, aa's 173-198) were tested for reactivity to the original serum from patient 1 (pt 1). (B) Recombinant proteins derived from one epitope clone aa's 173 to 198 were purified and subjected to Western blotting using the sera of AA patients who exhibited antibodies specific to the native DRS-1 protein. Patient 2 (pt 2) and patient 3 (pt 3) represent other PNH⁺ AA patients who showed high titers of DRS-1 Abs.