Human autoantibodies against a nucleolar protein.

Autoimmune sera showing prominent immunofluorescence in nucleolus were selected and analysed by immunoblotting techniques. Immunoblots using a nucleolar extract as antigen source revealed sera recognizing a 38 kDa nucleolar protein. Low concentration of Actinomycin D, which inhibits the ribosomal RNA synthesis, caused a loss of fluorescence. This suggests that the nucleolar antigen may be associated with the assembly of packaging of the ribosomes. The present nucleolar antigen has properties similar to the previously described nucleolar phosphoprotein B23 of rat cells and the recently described nucleolar protein NO38 of mouse and Xenopus cells.