CHARACTERIZATION OF RNA-BINDING DOMAINS OF HEPATITIS DELTA-ANTIGEN

Hepatitis delta antigen (HDAg), the only protein encoded by the hepati tis delta virus (HDV), binds specifically genomic and antigenomic stra nds of the HDV RNA. In a previous study, three recombinant HDAg subdom ains were synthesized, covering residues 11 to 78, 79 to 163 and 164 t o 212, and only the middle domain was shown to be responsible for the binding to HDV RNA. To investigate HDAg sequences involved in HDV RNA binding, we synthesized five peptides, 15 to 29 residues in length, an d tested their ability to bind HDV RNA using a simple non-radioactive ELISA with digoxigenin-labelled HDV genomic or antigenomic RNA probes. The specificity of interactions was demonstrated by comparison with c ontrol peptides and non-HDV RNA probes, and with an inhibition assay u sing recombinant HDAg. The HDAg-binding domain found within the middle region (79 to 163) of HDAg was more finely mapped: it is located betw een residues 79 and 107. In addition, another domain (residues 2 to 27 ) of HDAg was also found to bind specifically to HDV RNA. These two pe ptides share sequence similarities at residues 2 to 10 and 97 to 107 w ith other RNA-binding domains.