Hepatitis B virus (HBV) prevalent worldwide is of medical importance particularly because of it being the causative agent of chronic liver disease (including primary hepatocellular carcinoma) in humans (Szmuness, 1978). Together with those similar viruses found in woodchucks (Summers et al., 1978), ground squirrels (Marion et al., 1980) and Pékin ducks (Mason et al., 1980) they represent the hepadna virus group (Marion and Robinson, 1983). Due to inability to propagate them in tissue culture, details of mechanism of their replication still remain obscure. One of the unique features of these viruses is the structure of their DNA. The virions comprise of small circular double-stranded DNA molecules partly single stranded (Robinson et al., 1974), and a DNA ploymerase in the virion (Kaplan et al., 1973). Evidence in literature also suggests that the mechanism of replication of viral DNA is possibly unique and involves an RNA intermediate (Summers and Mason, 1982; Tiollais et al., 1988).
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