Viroids, Viruses, and RNA Silencing
The small RNA world just got bigger
By Leslie A. Pray
There is growing evidence that small RNAs, believed to play an antiviral
defense role in many organisms, may be acting as double agents. In March
2004, an international team of scientists reported that viroids, small
infectious particles of naked RNA, may be employing RNA-silencing machinery
to work their damage.1 Several weeks later, another international team
announced the discovery of microRNAs in the Epstein-Barr virus (EBV),
suggesting that miRNA-mediated gene suppression might play a role in
animal-virus pathogenicity.2 Many researchers say this is just the
beginning.

"In the past, all of these small RNAs were totally overlooked because they
are so small in size. If they got any attention at all, they were considered
unspecific degradation products. Now, we are starting to understand that
they represent a sort of cross-talk between viral or viroidal sequences and
endogenous genes," says Martin Tabler, Institute of Molecular Biology and
Biotechnology, Crete.

EBV, a large DNA virus responsible for mononucleosis and a number of other
diseases, including Burkitt lymphoma, is tough to beat; it hides from the
human immune system and infects for life. Rockefeller University's Sebastien
Pfeffer, lead author on the EBV study, says that he and his collaborators
were looking for evidence that animals defend against viral infection using
the same kind of posttranscriptional silencing pathways that plants,
insects, and other organisms use. But instead of antiviral RNA activity,
they discovered viral miRNA activity. According to Pfeffer, the data suggest
that miRNAs could be involved in tumor formation and may explain how EBV
hides so well. They also give scientists reason to look for miRNAs in other
viruses. Says Pfeffer: "miRNAs are found in practically every eukaryotic
organism. Other viruses could have them too."

Read the rest at TheScientist (Volume 18 | Issue 16 | 23 | Aug. 30, 2004)
http://www.the-scientist.com/yr2004/aug/research3_040830.html

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