Sequence of hepatitis B virus DNA incorporated into the genome of a human hepatoma cell line.

Seven copies of integrated hepatitis B virus (HBV) DNA and contiguous genomic DNA from a human hepatoma cell line (PLC/PRF/5) have been isolated by molecular cloning and have been partially sequenced. The HBV sequences are fragmented and rearranged. Thus, the surface antigen gene is the only intact HBV transcription unit present in these integrated sequences. The sites of integration-recombination are dispersed over the entire viral genome; there is some preference for integration within the double-stranded portion of the genome. There are no repeats at the ends of the integrated HBV DNA fragments. Thus, recombination does not take place in a manner resembling the integration of retroviruses. The sequence data suggest that each HBV fragment is of the adw subtype. However, the integrated DNAs show an unexpected degree of sequence divergence. Direct evidence for the duplication, transposition, and subsequent divergence of two sequences is presented. The data surprisingly suggest that infection-integration of four distinct adw strains occurred.