The comparative analysis of primary and secondary structures, and hydropathy plots of hepatitis B virus (HBV) and hepatitis delta virus (HDV) proteins was carried out. Two short regions belonging to the HBV terminal protein were shown to be homologous to two regions; one encoded by HDV ORF5, and the other encoded by small ORF of the HDV antigenomic RNA strand. We propose a new protein containing both these regions may be synthesized in HDV infected cells. Stiking structural homology between the terminal protein of HBV and this predicted protein called HDAg' of HDV may indicate a possible functional similarity.'We hypothesize the HDAg' may interact with and inhibit the polymerase activity of HBV.
