TRIM21, an autoantigen detected in 1988 in the sera of patients with autoimmune diseases (6), is a 52-kD protein as an antibody-binding protein of unusual structure by yeast two-hybrid analysis, whose molecular structural characterization and encoding genes indicate that it has no homology to the Ro60 protein, although both are considered to be the main antigenic targets of anti-Ro/SSA antibodies Figure 1 (7, 8). Here, RO60 is linked to autoimmune disease.