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The archaeal DNA folding, reported August 10 in Science, hints at the evolutionary origins of genome folding, a process that involves bending DNA and one that is remarkably conserved across all eukaryotes (organisms that have a defined nucleus surrounded by a membrane). Like Eukarya and Bacteria, Archaea represents one of the three domains of life. But Archaea is thought to include the closest living relatives to an ancient ancestor that first hit on the idea of folding DNA.
Scientists have long known that cells in all eukaryotes, from fish to trees to people, pack DNA in exactly the same way. DNA strands are wound around a "hockey puck" composed of eight histone proteins, forming what's called a nucleosome. Nucleosomes are strung together on a strand of DNA, forming a "beads on a string" structure. The universal conservation of this genetic necklace raises the question of its origin.
Eukaryotes - DNA - Bending - Style - Ancestor
If all eukaryotes have the same DNA bending style, "then it must have evolved in a common ancestor," says study coauthor John Reeve, a microbiologist at Ohio State University. "But what that ancestor was, is a question no-one asked."
Earlier work by Reeve had turned up histone proteins in archaeal cells. But, archaea are prokaryotes (microorganisms without a defined nucleus), so it wasn't clear just what those histone proteins were doing. By examining the detailed structure of a crystal that contained DNA bound to archaeal histones, the new study reveals exactly how DNA packing works.
Luger - Colleagues - Crystals - Histone-DNA - Complex
Luger and her colleagues wanted to make crystals of the histone-DNA complex in Methanothermus fervidus, a heat-loving archaeal species. Then, they wanted to bombard the crystals with X-rays. This technique, called X-ray crystallography, yields precise information about the position of each and every amino acid and nucleotide in the molecules being studied. But growing the crystals was tricky (the histones would stick...
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