Immunodominant RNA recognition motifs of human nucleolin/C23.

Nucleolin/C23 is a nucleolar phosphoprotein implicated in the synthesis, processing and transport of ribosomal RNA and gene transcription. Auto-antibodies to human nucleolin/C23 have been reported in patients with systemic lupus erythematosus and other systemic autoimmune disorders. To identify immunodominant regions in nucleolin/C23, deletion fragments of nucleolin/C23 were fused in frame with the glutathione S-transferase gene. Seven monoclonal anti-nucleolin/C23 antibodies were used to determine the immunoreactivity of the bacterially expressed fusion proteins. Two sets of immunogenic regions at amino acids 314-389 and 387-461 were identified; each contained overlapping discontinuous epitopes and a centrally located RNA recognition motif. An auto-immune serum from a patient with systemic lupus erythematosus patient was found to contain antibodies against human nucleolin/C23 which recognized amino acids 387-461 of nucleolin/C23.