A NUCLEOLAR RNA HELICASE RECOGNIZED BY AUTOIMMUNE ANTIBODIES FROM A PATIENT WITH WATERMELON STOMACH DISEASE

Watermelon stomach is characterized by prominent stripes of ectatic va scular tissue in the stomach similar to stripes on a watermelon; in pa tients with this disorder chronic gastrointestinal bleeding occurs and approximately half of these patients have associated autoimmune disor ders, In the serum of one patient, an antinucleolar antibody titer of 1:25 600 was found; the antibodies specifically recognized a similar t o 100 kDa nucleolar protein, which we referred to as the 'Gu' protein, Its cDNA was cloned and sequenced, The Gu protein is a member of a ne w subgroup of RNA helicases, the DEXD box family, Gu protein fused wit h glutathione S-transferase contains ATP-dependent RNA helicase activi ty which preferably translocates in the 5'-->3' direction, Its RNA fol ding activity, RNA-dependent ATPase and dATPase activities, and its tr anslocation direction are similar to those of RNA helicase II [Flores- Rozas,H. and Hurwitz,J. (1993) J. Biol, Chem, 268, 21372-21383], Seque ncing of 209 amino acids of RNA helicase II peptides showed 96.7% iden tity with the cDNA-derived amino acid sequence of the Gu protein, The precise biological roles of this RNA helicase in the biogenesis of rib osomal RNA and the pathogenesis of watermelon disease and autoimmune d isorder require further study.