Sequence homology between retroviral reverse transcriptase and putative polymerases of hepatitis B virus and cauliflower mosaic virus

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Abstract
In infected cells, the RNA genomes of RNA tumour viruses are copied into DNA by a virus-encoded reverse transcriptase enzyme1–3. This transfer of information from RNA into DNA was thought to be a unique feature of RNA tumour viruses3, but recent results suggest it may be a more general strategy. Hepatitis B virus (HBV) has a double-stranded DNA genome, and it has recently been shown that the minus DNA strand of the HBV genome is copied from a plus-strand RNA template, leading to the suggestion that reverse transcription is central to the life cycle of HBV4–6. More recently it has been suggested that the replication cycle of a plant virus, cauliflower mosaic virus (CaMV), includes a reverse transcription step7–9. We report here the existence of amino acid sequence homology between retroviral reverse transcriptase and the putative polymerases of HBV and CaMV.