RNA interference, or RNAi, is a technique that cells use to fight off viruses. Some viruses store their genetic material in the form of RNA, and as the virus replicates in a cell, small doubled-over fragments of the virus's RNA are produced. A folded-over strand of RNA floating inside a cell indicates that that cell is infected, and the strand is part of the virus's genome. So the cell will try to suppress viral replication by suppressing any protein manufacture which uses that sequence.
Although RNAi was discovered only recently, scientists recognized that it could provide a new way to control which genes are expressed in a cell. Simply make an RNA fragment that contains part of the gene you want to knock out, introduce it to the cell, and the cell will shut down its own production of the corresponding protein just as though the RNA fragment had come from a virus.
Now it turns out that viruses have beaten us to this trick. The Epstein-Barr virus is a DNA virus, presumably more highly evolved than RNA viruses. But it contains five genes that produce double-stranded RNA, and these strands switch off expression of certain genes in the host cell. Guess what -- these genes appear to be ones that would help the cell respond to the virus. And guess what else -- the list includes the tumor-fighting gene p53. This could explain how this virus can promote certain cancers.
A virus turning a cell's anti-virus mechanism against itself -- what won't nature think up next?
Chris Phoenix
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