title: Characterization of the DNA-binding protein antigen Ku recognized by autoantibodies from patients with rheumatic disorders.
abstract: We have characterized the biochemical nature of the Ku protein, the antigen recognized by autoantibodies from certain patients with scleroderma-polymyositis overlap syndrome. From extracts of HeLa cells labeled with [32P]orthophosphate, anti-Ku antibodies precipitated a high molecular weight nucleic acid identified as DNA because of sensitivity to DNase I and resistance to RNase. From extracts of cells labeled with [35S] methionine, these antibodies precipitated two polypeptides of 70,000 and 80,000 Da. These proteins were purified using immunoaffinity column chromatography. In immunoblots most sera containing anti-Ku antibodies recognized both Ku proteins but one serum bound only to the 70,000-Da subunit. When nucleosomal segments of chromatin were used as antigen, anti-Ku antibodies precipitated dinucleosomes and larger forms of chromatin but not mononucleosomes. Thus, the Ku antigen is a novel DNA-binding protein that is at least partially exposed on nucleosomal segments of chromatin.
mesh_terms: D034961:Antigens, Nuclear; D000954:Antigens, Surface / Q000276:immunology / Q000302:isolation & purification* / Q000378:metabolism; D001323:Autoantibodies / Q000276:immunology; D002843:Chromatin / Q000032:analysis / Q000648:ultrastructure; D002846:Chromatography, Affinity; D004247:DNA / Q000378:metabolism; D004265:DNA Helicases; D004268:DNA-Binding Proteins / Q000276:immunology / Q000302:isolation & purification* / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D006367:HeLa Cells / Q000032:analysis; D006801:Humans; D000072200:Ku Autoantigen; D009220:Myositis / Q000276:immunology / Q000378:metabolism*; D009707:Nucleosomes / Q000276:immunology; D011233:Precipitin Tests; D012595:Scleroderma, Systemic / Q000276:immunology / Q000378:metabolism*
chemical_list: D034961:Antigens, Nuclear; D000954:Antigens, Surface; D001323:Autoantibodies; D002843:Chromatin; D004268:DNA-Binding Proteins; D009707:Nucleosomes; D004247:DNA; D004265:DNA Helicases; C106893:XRCC5 protein, human; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen