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First field test of engineered virus.

First field test of engineered virus

Researchers plan to begin the United States' first open-field test of a genetically engineered virus, starting in late July. Scientists from the Boyce Thompson Institute for Plant Research and Cornell University will spray genetically weakened viruses onto cabbage plants at Cornell's agricultural experiment station in Geneva, N.Y. they expect the viruses to infect and kill cabbage looper caterpillars. The Environmental Protection Agency approved the test June 12.

Scientists want to weaken the virus because a potent viral insecticide would be unsafe if it persisted in the environment.

To weaken the virus -- one of a group of insect parasites called baculoviruses--the researchers removed a gene coding for a protein called polyhedrin, which shields the micro-organisms against environmental damage. Early in an infection, baculoviruses replicate and spread from cell to cell as single particles. The polyhedrin gene normally switches on late in the infection, forcing the host cell to produce large quantities of polyhedrin. New virus particles become embedded in masses of polyhedrin, like raisins in raisin bread. Eventually the cell becomes engorged with polyhedrin capsules and bursts. After several days, the insect dies and the capsules disperse. The cycle begins again when a looper eats encapsulated viruses along with its cabbage.

Laboratory tests show that without the protective protein, "this virus doesn't have a prayer," says H. Alan Wood, project leader at Boyce Thompson in Ithaca, N.Y.

Wood first infects insect cells in vitro with a mixture of normal and altered viruses. Both end up embedded in polyhedrin produced by normal virus. After spraying the virus capsules on the cabbage, the scientists will monitor the rate at which altered viruses disappear. Wood predicts their levels will drop to undetectable amounts within two years. Some altered viruses in the lab appear to have regained the ability to trigger polyhedrin production, but the researchers are unable to detect such recombinants after several generations, he says.

If removing the gene debilitates the virus, says Wood, the finding could pave the way for making a faster-acting but still short-lived baculovirus--a melting magic bullet.
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Title Annotation:Biology
Publication:Science News
Date:Jul 15, 1989
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