Immunoprecipitation of replication protein A (RPA). (a) Immunoprecipitation of RPA by mAbs and human autoimmune sera. 35S-labeled K562 cell extracts were immunoprecipitated with mAbs against RPA32 (lane 32), human sera with anti-RPA (lanes 1 to 4, SLE; lanes 5 to 8, others) or with normal human serum (NHS). Coexisting anti-Ro (lane 2) and anti-Su (lanes 3 and 8) are indicated by the open arrowheads. (b) Immunoprecipitation of lupus autoantigens that co-migrate or overlap with RPA. [35S]-labeled K562 cell extracts were immunoprecipitated with sera from patients with SLE (lanes labeled Ki to Histones except lane Ku) or PM (lane Ku), or mouse mAbs BM6.5 (anti-histones). These sera or mAbs recognize autoantigens co-migrate with components of RPA. RPA32 co-migrates with Ki (SL, lanes Ki and rP/Ki/his) and U1snRNP-A (U1-A, lanes nRNP and Ku/nRNP), RPA70 co-migrates with Ku p70 (lanes Ku/nRNP and Ku), and RPA14 co-migrates with histone H4 (lanes rP/Ki/his, Histones, and BM6.5). The specificities of human autoimmune sera are indicated. The numbers at the right are the molecular masses of protein standards. his, histones; rP, ribosomal P.