STABLE EXPRESSION OF HEPATITIS DELTA VIRUS-ANTIGEN IN A EUKARYOTIC CELL-LINE

The gene encoding the hepatitis delta virus structural antigen (HDAg) was linkd 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(r) in the range of 7 x 105 to 2 x 106, which appeared to contain conformation-dependent epitopes, whereas the density of the antigen was 1.19 g/ml by equilibrium centrifugation in caesium chloride, and in rate zonal centrifugaton it sedimented with a value of 50S, close to that of particulate hepatitis B virus surface antigen. Immunoblotting demonstrated a single polypeptide with an M(r) of 24K which corresponded 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 antigenomic species of hepatitis delta virus RNA.