In fly DNA, the footprint of a fly virus

In fly DNA, the footprint of a fly virus | e! Science News

 In a curious evolutionary twist, several species of a commonly studied fruit fly appear to have incorporated genetic material from a virus into their genomes

The study found that several types of fruit fly -- scientific name Drosophila -- harbored genes similar to those that code for the sigma virus, a fly virus in the same family as rabies. The authors believe the genetic information was acquired during past viral infections and passed on from fruit fly parent to offspring through many generations.

The discovery could open the door for research on why flies and other organisms selectively retain viral genes -- dubbed "fossil" genes -- through evolution

One hypothesis is that viral genes provide an anti-viral defense, but scientists have had trouble testing this theory because viral genes found in animals are often millions of years old -- ancient enough that the genes' genetic sequence differs significantly from that of modern-day viruses.

The new study, in contrast, uncovered a viral gene that appears to be relatively young, with genetic material closely mirroring that of a modern sigma virus.

The sigma virus belongs to a class of RNA viruses that lack an important enzyme, reverse transcriptase, that enables other viruses to convert their genetic material into DNA for integration into host genomes.

The new study supplies one possible answer, suggesting that viruses may use reverse transcriptase present in host cells to facilitate incorporation of viral genes into host DNA.

The position and context of the viral gene suggests that the retrotransposon made a copying error and copied and pasted virus genes into the fly genome. This is the clearest evidence yet that non-retroviral RNA virus genes naturally enter host genomes by the action of enzymes already present in the cell