Patients with primary biliary cirrhosis (PBC) frequently have autoantibodies 
against a 210-kD integral glycoprotein of the nuclear envelope pore membrane. 
This protein, termed gp210, has a 1,783-amino acid amino-terminal domain located 
in the perinuclear space, a 20-amino acid transmembrane segment, and a 58-amino 
acid cytoplasmic carboxy-terminal tail. We now demonstrate that autoantibodies 
from 25 patients with PBC that recognize gp210 react with the cytoplasmic 
carboxy-terminal tail while none react with unmodified linear epitopes in the 
amino-terminal domain. The epitope(s) recognized by autoantibodies from all 25 
patients is contained within a stretch of 15 amino acids. The recognized amino 
acid sequence is homologous to the protein products of the Escherichia coli mutY 
gene and Salmonella typhimurium mutB gene with an exact identity of six 
consecutive amino acids, suggesting that anti-gp210 antibodies may arise by 
molecular mimicry of bacterial antigenic determinants.