Abstract

A novel nucleolus protein has been identified and cloned using human autoimmune serum. Its cDNA and amino acid sequences have been determined and are disclosed. This antigenic protein, termed ASE-1, has an approximate molecular mass of 55 kDa. Immunoblot analysis indicates that both the native protein and the in vitro translation products of the cDNA migrate on SDS-PAGE at an apparent molecular mass of 90 kDa. Indirect immunofluorescence analysis using antibodies generated to cloned regions of ASE-1 indicates that this protein occurs at the fibrillar centers of the nucleolus in the putative sites of rDNA transcription. During cell division ASE-1 localizes to the nucleolus organizer regions of the chromosomes, where it is closely associated with RNA polymerase 1. As an autoantigenic nucleolar protein, ASE-1 has been found to be a reliable serum marker for systemic lupus erthyematosus (SLE). This finding makes ASE-1 useful in the clinical detection and characterization of the disease. To identify the presence of SLE in an individual patient, a serum samples is taken and screened against the cloned ASE-1 protein to identify sera with anti-ASE-1 autoantibodies. This screening can be done using an ELISA assay, western blot techniques, or by binding the antigen to microspheres and identifying reactive sera by flow cytometry.