Georg Reimer, Ulrich Scheer, Jan-Michael Peters, Eng M. Tan

• Precipitating anti-PM-Sel antibodies are present in sera from patients with polymyositis. scleroderma. and polymyositis/scleroderma overlap syndromes. By indirect immunofluorescence microscopy. anti-PM-Scl antibodies stained the nucleolus in cells of different tissues and species. suggesting that the antigen is highly conserved. By electron microscopy, anti-PM-Scl antibodies reacted primarily with the granular component of the nuc1eolus. Drugs that inhibit rRNA synthesis had a marked effect on the expression of PM-Scl antigen. In actinomycinPrecipitating anti-PM-Sel antibodies are present in sera from patients with polymyositis. scleroderma. and polymyositis/scleroderma overlap syndromes. By indirect immunofluorescence microscopy. anti-PM-Scl antibodies stained the nucleolus in cells of different tissues and species. suggesting that the antigen is highly conserved. By electron microscopy, anti-PM-Scl antibodies reacted primarily with the granular component of the nuc1eolus. Drugs that inhibit rRNA synthesis had a marked effect on the expression of PM-Scl antigen. In actinomycin D-treated cells, immunofluorescence staining by anti-PM-Scl was signüicantly reduced with residual staining restricted to the granular regions of nuc1eoli. Treatment with 5,6-dichloro-beta-D- ribofuranosylbenzimidazole (DRB) also selectively reduced nuc1eolar staining. On a molecular level, anti-PM-Sel antibodies precipitated 11 polypeptides with molecular weights (Mr) ranging from 110,000 to 20,000. The Mr 80,000 and 20.000 polypeptides were phosphorylated. Evidence suggests that the PM-Scl antigen complex may be related to a prerlbosomal particle.…