THE I-PROTEIN OF THE HETEROGENEOUS NUCLEAR RIBONUCLEOPROTEIN COMPLEX IS A NOVEL DOG NUCLEAR AUTOANTIGEN

In eukaryotic cells, heterogeneous nuclear RNA is associated with a se t of abundant nuclear proteins to form complex ribonucleoprotein struc tures (hnRNP). Autoantibodies to hnRNP G protein have been previously reported in German shepherd dogs with lupus-like syndrome. In the pres ent study, we describe the characterization of a novel antigen recogni zed by a serum from a schnauzer dog with a non-erosive polyarthritis. The autoantibodies give, by indirect immunofluorescence,a nuclear patt ern with staining close to one of the nucleoli. Immunoblotting and imm unoprecipitation data reveal that the autoantigens are in fact two clo sely related basic proteins (average pI 8.7) with apparent molecular w eights of 56 kDa (p56) and 59 kDa (p59). The results of immunoprecipit ation with anti-hnRNP antibodies and DNA affinity column chromatograph y strongly suggest that these autoantigens correspond to hnRNP I prote ins. This point was confirmed by cloning and sequencing a cDNA clone e ncoding the complete sequence of the antigens. In addition, we found t hat anti-hnRNP I antibodies preferentially stain certain loops of the Pleurodeles waltl lampbrush chromosomes. These data, added to previous ones on anti-p43/hnRNP G protein in German shepherd dogs with lupus-l ike syndrome, confirm the interest of this-category of antibodies to h nRNP proteins in autoimmune disorders. (C) 1996 Academic Press Limited