Autoantibodies from systemic rheumatic disorders have become useful reagents in molecular biology. SS-B/La, a major target of autoantibodies in lupus and Sjogren's syndrome, has been identified as a 46 kDa protein component of a ribonucleoprotein (RNP) particle implicated in the maturation of RNA polymerase III transcripts. This report describes the complete sequences of human and bovine SS-B/La and the identification of RNA-binding protein consensus sequences RNP1 and RNP2 in the N-terminal region previously shown to be complexed with RNA in UV-crosslinking experiments. Segments of about 95 residues from the RNA-binding domain of SS-B/La and from 29 RNA-binding domains of several other proteins are analysed with respect to the frequency of amino acids and their hydrophobicity at each position. The data suggest that SS-B/La belongs to a large family of RNA-binding proteins which includes heterogeneous nuclear RNPs, nucleolin, mRNA polyadenylate binding protein, and small nuclear RNPs.