For many years we have assumed that all retroviruses replicate by a uniform major strategy. Given that, a paper in last week's Science provides pause for thought — it shows that the spumavirus human foamy virus (HFV) differs from oncoviruses (such as mouse leukaemia virus, MLV) and lentiviruses (such as HIV) in carrying full-length, double-stranded DNA genomes in a proportion of virus particles. Furthermore, HFV reverse transcriptase and other Pol proteins are translated from a spliced messenger RNA, and lack Gag sequences. These findings are unexpected and provocative; HFV resembles hepatitis B virus, which has a DNA genome, in these respects as much as it does retroviruses. Moreover, other reports suggest that HFV is not so human after all, but may serve as a useful gene vector to non-proliferating cells.
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