Analysis of autoantibodies to RNA helicase A (RHA). (a) Immunoprecipitation using anti-RHA-positive sera. Immunoprecipitation of 35S-methionine-labeled K562 cell extract by anti-RHA-positive sera from Mexican patients with systemic lupus erythematosus (SLE) (n = 14), anti-RHA prototype serum (lane RHA), and a normal human serum (NHS) is shown. Number of years between initial diagnosis and anti-RHA test of each patient is indicated below the lanes. Positions of RHA, UsnRNP components A, B'/B, U5-200k doublet, Ku (p70 and p80), Ro 60k, and ribosomal P P0, and molecular weight (MW) are indicated. Positivity of anti-Sm and U1RNP is indicated at the top. White arrowheads indicate major degradation products of RHA. (b) Immunoprecipitation and Western blot confirmation of anti-RHA. K562 cell extract was immunoprecipitated by sera positive for the 140-kDa protein that co-migrated with RHA. Identity of the 140-kDa protein as RHA was validated by Western blot using a rabbit anti-RHA serum. Lane RHA, anti-RHA prototype serum; lanes 1 to 6, anti-RHA-positive sera screened by immunoprecipitation; lanes 7 to 9, NHS.