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Proc Natl Acad Sci U S A. 1999 Jul 6;96(14):8022-7.

Evidence that a plant virus switched hosts to infect a vertebrate and then recombined with a vertebrate-infecting virus.

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  • 1Bioinformatics, Research School of Biological Sciences, The Australian National University, G.P.O. Box 475, Canberra 2601, Australia. mgibbs@rsbs.anu.edu.au

Abstract

There are several similarities between the small, circular, single-stranded-DNA genomes of circoviruses that infect vertebrates and the nanoviruses that infect plants. We analyzed circovirus and nanovirus replication initiator protein (Rep) sequences and confirmed that an N-terminal region in circovirus Reps is similar to an equivalent region in nanovirus Reps. However, we found that the remaining C-terminal region is related to an RNA-binding protein (protein 2C), encoded by picorna-like viruses, and we concluded that the sequence encoding this region of Rep was acquired from one of these single-stranded RNA viruses, probably a calicivirus, by recombination. This is clear evidence that a DNA virus has incorporated a gene from an RNA virus, and the fact that none of these viruses code for a reverse transcriptase suggests that another agent with this capacity was involved. Circoviruses were thought to be a sister-group of nanoviruses, but our phylogenetic analyses, which take account of the recombination, indicate that circoviruses evolved from a nanovirus. A nanovirus DNA was transferred from a plant to a vertebrate. This transferred DNA included the viral origin of replication; the sequence conservation clearly indicates that it maintained the ability to replicate. In view of these properties, we conclude that the transferred DNA was a kind of virus and the transfer was a host-switch. We speculate that this host-switch occurred when a vertebrate was exposed to sap from an infected plant. All characterized caliciviruses infect vertebrates, suggesting that the host-switch happened first and that the recombination took place in a vertebrate.

PMID:
10393941
PMCID:
PMC22181
[PubMed - indexed for MEDLINE]
Free PMC Article
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