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Ancient Protein Sequenced
14 November 2002 (All day)
Paleontologists would love to use DNA to study the evolution of long-extinct animals, but genetic material is much too fragile to last very long. Now, scientists have tapped a related, sturdier source of molecular information by studying proteins in fossilized bone. Two bison bones more than 55,000 years old have yielded the first complete amino acid sequences from a fossil, and researchers think the same technique could work for much older specimens.
Biochemist Christina Nielsen-Marsh of the University of Newcastle, U.K., and her colleagues borrowed a technique used to analyze modern genetic material and applied it to bison bones recovered from the permafrost of Siberia and Alaska. In the December issue of Geology, the team members report that they isolated a protein called osteocalcin from the bones and recovered the first intact amino acid sequences from an ancient specimen. Because the protein sequence is directly related to the DNA code, the team says that comparing protein sequences--like comparing DNA sequences--is an approach that can be used to determine degrees of relatedness between species and to decipher how ancient animals evolved.
In addition, proteins have distinct advantages over DNA, says Nielsen-Marsh. Osteocalcin is bound tightly to minerals in the bone, which makes them very stable. Although DNA can survive only up to 100,000 years and is rarely found in useful quantities in specimens even half that old, the team has found measurable amounts of osteocalcin in 120,000-year-old bones. Nielsen-Marsh estimates that the proteins might survive as long as 10 million years. Their stability makes osteocalcin more likely to endure warmer, harsher environments as well. Contamination--one of the biggest concerns with ancient DNA analyses--is also less likely to be a problem with osteocalcin, because it is found only in vertebrate bones.
"It's a very promising preliminary result," says evolutionary biologist Robert Wayne of the University of California, Los Angeles. By providing an alternative to DNA, osteocalcin could expand the range of specimens that can be used to test evolutionary hypotheses, he says.