It covers nearly 80% of the genome and overlaps the other three ORFs. The product to the Pol gene is a multifunctional protein spanning approxmately 834 to 845 codons and comprises the DNA- and RNA- dependent DNA polymerase (reverse transcriptase, RT), RNase H and the terminal protein domains (Bartenschlager and Schaller, 1988; Radziwill et al., 1990) (Figure-1.6A). The terminal protein, or primase, is located at the N-terminus of the polymerase and separated from the DNA polymerase domain by a non-essential spacer region. It is covalently bound to the 5’ end of the minus DNA strand and is involved in protien priming during reverse transcription (Wang and Seeger, 1992). The C-terminus portion of the polypeptide is responsible for genome replication, comprising of the viral polymerase which is involved in reverse transcription of pregenomic RNA (pgRNA) to minus strand and DNA-dependent-DNA polymerse to form the plus strand. There is recent evidence demonstrating the presence of pyrophosphorolytic activity in DHBV whereby incorporated dNTPs are removed from the elongating DNA by the reverse process of DNA polymerisation: DNAn + dNTP Ppi (Urban et al., 2001). It is possible that the ability of DHBV RT to remove recently incorporated dNTP by pyrophosphorolysis during viral replication may be a way to remove incorrectly incorporated dNTP, and thus function as a surrogate 3`-5` exonuclease activity. Finally,…