The Ro small cytoplasmic ribonucleoproteins: identification of the antigenic protein and its binding site on the Ro RNAs.

Abstract

Patients with systemic lupus erythematosus and other rheumatic diseases often possess autoantibodies directed against discrete classes of small ribonucleoprotein particles (RNP). The class of particles recognized by anti-Ro antibodies contains from 2 to 4 small cytoplasmic RNA, depending on the mammalian species examined. An antigenic polypeptide of 60 kDa [kilodalton] is the major protein residing in Ro RNP from human HeLa [human cervical carcinoma] cells. To determine what common feature of Ro RNA sequence or structure is recognized by the Ro protein, ribonuclease protection experiments were carried out on isolated Ro RNP from HeLa cells. For each of the 3 human Ro RNA whose sequence is known, the most highly protected portion found in immunoprecipitates corresponded to the lower section of a stem formed by base-pairing the 5'' and 3'' ends of the RNA. Within this protected helix is a highly conserved region composed of 7 identical base pairs with a single bulged cytidine. Possible functions for the Ro RNP are discussed.