Non-Human DNA Left By Ancient Viruses Found In Human Genome

A team of researchers at the Tufts University and the University of Michigan Medical School have found 19 new pieces of non-human DNA in human genome. As per their findings published in the Proceedings of the National Academy of Sciences, these new pieces of non-human DNA was left by viruses, called Human Endogenous RetroViruses (HERVs), that first infected our ancestors hundreds of thousands of years ago.

The team also discovered that one stretch of newfound DNA – found in about 50 of the 2,500 people they studied – contains an intact, full genetic recipe for an entire virus. They are not sure whether the virus can replicate or reproduce, but studies of ancient virus DNA have shown it can affect its human carriers.

The reason why this non-human DNA ended up in genomes of modern humans today is that these viruses succeeded in leaving behind DNA-based replica of their RNA genetic material into our ancestors’ genomes. And over generations, this DNA kept getting copied and handed down when humans reproduced. The study confirms that our DNA is not fully human as about 8 percent of it actually came from viruses.

Researchers say these new HERVs are part of the same type of virus that includes the modern human immunodeficiency virus, which causes AIDS, and they are part of the family called HERV-K. This is the only the second intact provirus found hiding in human DNA.

“This one looks like it is capable of making infectious virus, which would be very exciting if true, as it would allow us to study a viral epidemic that took place long ago,” says John Coffin, Ph.D. of the Tufts University School of Medicine, in a news release. “This research provides important information necessary for understanding how retroviruses and humans have evolved together in relatively recent times.”

“Many studies have tried to link these endogenous viral elements to cancer and other diseases, but a major difficulty has been that we haven’t actually found all of them yet,” says co-first author Zachary H. Williams. “A lot of the most interesting elements are only found in a small percentage of people, which means you have to screen a large number of people to find them.”

“This is a thrilling discovery,” says co-first author Julia Wildschutte. “It will open up many doors to research. What’s more, we have confirmed in this paper that we can use genomic data from multiple individuals compared to the reference human genome to detect new HERVs. But this has also shown us that some people carry insertions that we can’t map back to the reference.”

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