The viruses can cause us many problems, from annoying to deadly ones, but we shouldn't be angry at our relatives - 8 percent of human DNA comes from viruses!
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A recent study on the human DNA was just "a usual one", dealing with DNA, genomes and stuff but then something unexpectedly came up: 8 percent of DNA we humans got from viruses. The study revealed that the genomes of humans and other mammals contain DNA derived from the insertion of viruses whose replication takes place in the nucleus of cells. It was the first to show sequences derived from a virus other than retroviruses. Researchers have known since 2001 that 8 percent of human genetic material is derived from retroviruses.
The assimilation of viral sequences into the host genome is a process called endogenization. This occurs when viral DNA integrates into a chromosome of reproductive cells and is subsequently passed from parent to offspring. Until now, retroviruses were the only viruses known to generate such copies in vertebrates. But the scientists now have found that non-retroviral viruses called bornaviruses have been endogenized repeatedly in mammals throughout evolution.
Bornavirus (BDV) are called after the town of Borna in Germany where a virus epidemic in 1885 wiped out a regiment of cavalry horses. BDV infects a range of birds and mammals, including humans. It is unique because it infects only neurons, establishing a persistent infection in its host's brain, and its entire life cycle takes place in the nucleus of the infected cells.
This intimate association of BDV with the cell nucleus prompted researchers to investigate further. They unearthed a huge number of endogenous Borna-like N elements in many diverse mammals. The scientists also were able to recover spontaneous BDV insertions in the chromosomes of human cultured cells persistently infected by BVD. Based on these data, they proposed that BDV insertions could be a source of mutations in the brain cells of infected individuals.
So, next time you get flu don't be very angry, you are under attack of our relatives. ■