Stable expression of hepatitis delta virus antigen in a eukaryotic cell

The gene encoding the hepatitis delta virus structural antigen (HDAg) was linked to a neomycin resistance gene in a retrovirus expression vector, and human HepG2 cells were transfected with the recombinant plasmid. A stable cell line was cloned that expressed HDAg in the nuclei of 100 % of cells, in a pattern indicating a close relationship with cell nucleoli. Analysis of partially purified recombinant HDAg by HPLC showed an M ~ in the range o f7x l05 to 2x 10 6, which appeared to contain conformation-dependent epitopes, whereas the density of the antigen was 1.19 g/ml by equilibrium centrifugation i caesium chloride, and in rate zonal centrifugation it sedimented with a value of 50S, close to that of particulate hepatitis B virus surface antigen. Immunoblotting demonstrated a single polypeptide with an Mr of 24K which corres-ponded to the smaller of the two HDAg-specific polypeptides present in infected sera. The recombinant HDAg polypeptide was shown to be a RNA-binding protein with specificity for both genomic and anti-genomic species of hepatitis delta virus RNA