Evidence that the human foamy virus genome is DNA

The genomes of the spumaviruses, of which human foamy virus (HFV) is the pr ototype, are very similar to those of other complex retroviruses, However, in some aspects of the viral replicative cycle, HFV more closely resembles pararetroviruses such as hepatitis B virus, Previous work indicated that HF V extracellular particles contain apparently full-length double-stranded DN A, as well as RNA. We have further characterized the amount of DNA in parti cles and the role that this DNA has in viral replication. Experiments with the reverse transcriptase inhibitor 3'-azido-3'-deoxythymidine (AZT) sugges t that reverse transcription is largely complete before extracellular virus infects new cells. In addition, we have been able to show that DNA extract ed from virions can lead to production of virus after transfection. Taken t ogether, these data suggest that complete, or nearly complete, proviral-len gth DNA is present in viral particles and that this DNA is sufficient for n ew rounds of viral replication.