About 8% of human genetic material comes from viruses.
Nineteen new pieces of non-human DNA – left by viruses that first infected our ancestors hundreds of thousands of years ago – have just been found, lurking between our own genes.
And one stretch of newfound DNA, found in about 50 of the 2,500 people studied, contains an intact, full genetic recipe for an entire virus, say the scientists who published their findings in the Proceedings of the National Academy of Sciences.
Whether or not it can replicate, or reproduce, it isn’t yet known. But other studies of ancient virus DNA have shown it can affect the humans who carry it.
In addition to finding these new stretches, the scientists also confirmed 17 other pieces of virus DNA found in human genomes by other scientists in recent years.
The study looked at the entire span of DNA, or genome, from people from around the world, including a large number from Africa – where the ancestors of modern humans originated before migrating around the world. The team used sophisticated techniques to compare key areas of each person’s genome to the “reference” human genome.
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The findings add to what science already knows about human endogenous retroviruses, or HERVs. That’s the name for the ancient infectious viruses that inserted a DNA-based copy of their own RNA genetic material into our ancestors’ genomes. They’re part of the same type of virus that includes the modern human immunodeficiency virus, which causes AIDS.
Over generations, the virus-generated DNA kept getting copied and handed down when humans reproduced. That’s how it ended up in our DNA today. In fact, about 8 percent of what we think of as our “human” DNA actually came from viruses. In some cases, HERV sequences have been adopted by the human body to serve a useful purpose, such as one that helps pregnant women’s bodies build a cell layer around a developing fetus to protect it from toxins in the mother’s blood.
The new HERVs are part of the family called HERV-K. The intact whole viral genome, or provirus, just found was on the X chromosome; it’s been dubbed Xq21. It’s only the second intact provirus found to be hiding in human DNA.
In the researchers’ own words: “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 senior author and virologist John Coffin, Ph.D. of the Tufts University School of Medicine. “This research provides important information necessary for understanding how retroviruses and humans have evolved together in relatively recent times.”
from Stowe Boyd http://stoweboyd.com/post/141596498592
