Friday, June 22, 2007

Science News


Researchers exploring the chromosomes of the modern chimpanzee have discovered an amazing tale in the DNA -- evidence of an ancient battle with a retrovirus against which early human beings and apes evolved different defenses.

That battle left chimps, gorillas and old world monkeys vulnerable to the virus 4 million years ago, but our human forebears evolved instead a natural antiviral protein that protected against it.

That evolutionary path, which gave us immunity to the ancient virus, nevertheless may have made human beings -- and not apes - vulnerable to the modern scourge of HIV.

Such are the startling conclusions of a study published in Friday's issue of the journal Science by researchers at the Fred Hutchison Cancer Research Center in Seattle.

"We did a really great job 4 million years ago, but now we have a major new retrovirus to deal with,'' said Shari Kaiser, a Fred Hutchison researcher and lead author of the report.

Her findings are the latest in the burgeoning new field of paleovirology, in which scientists have found etched into the genes of plants and animals something akin to a medical record that dates back millions of years.

"It is an absolutely fascinating story in evolutionary biology,'' said Dr. Warner Greene, director of the Gladstone Institute for Virology in San Francisco. Greene had seen a presentation of the study at an academic conference earlier this year.

The virus responsible for this ancient mayhem is long extinct, but Kaiser and her colleagues made their case by resurrecting a living version of it using the genetic instructions planted by the bug into the chimpanzee genome about 4 million years ago.

Retroviruses are a primitive microbes containing their own genetic information in a single strand of RNA -- a flimsier chain of molecules than DNA, but one that is able to transmit instructions on how to make proteins or copies of itself.

When a retrovirus infects a cell, it plants a copy of its genetic instructions directly into the genes of the cell it has invaded. These instructions, which are also converted into more stable DNA, can be passed down through generations if an egg cell, for example is infected. HIV is a retrovirus. So was this ancient bug, Pan troglodyte endogenous retrovirus, which scientists call PtERV, or PERV for short.

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