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Originally Posted by By ANDREW POLLACKMARCH. New York Times 3 March 2014
In the late 1980s, scientists at Osaka University in Japan noticed unusual repeated DNA sequences next to a gene they were studying in a common bacterium. They mentioned them in the final paragraph of a paper: “The biological significance of these sequences is not known.”
Now their significance is known, and it has set off a scientific frenzy.
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In the past year or so, researchers have discovered that the bacterial system can be harnessed to make precise changes to the DNA of humans, as well as other animals and plants.
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The sequences, it turns out, are part of a sophisticated immune system that bacteria use to fight viruses. And that system, whose very existence was unknown until about seven years ago, may provide scientists with unprecedented power to rewrite the code of life.
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Scientists must synthesize a strand of DNA’s chemical cousin RNA, part of which matches the DNA sequence to be sliced. This “guide RNA” is attached to a bacterial enzyme called Cas9. When the guide RNA binds to the corresponding DNA sequence, Cas9 cuts the DNA at that site.
The cell tries to repair the cut but often does so imperfectly, which is enough to disable, or knock out a gene. To change a gene, scientists usually insert a patch — a bit of DNA similar to where the break occurred but containing the desired change. That patch is sometimes incorporated into the DNA when the cell repairs the break.
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Article including graphics here in New York Times -
http://www.nytimes.com/2014/03/04/he...-dna.html?_r=0