For all the furious hype around the gene-editing tool Crispr/Cas9, no one has ever really seen it in action. Like really seen it. How the protein Cas9 unzips a strand of DNA, how it slips in the molecule that guides it to a target—and finally, how it goes snip snip on the DNA. The power of Crispr/Cas9 is its ability to do this all so precisely and reliably.
How can you see something as small as a protein anyway? For decades, that has meant coaxing proteins to grow into crystal structures. Scientists then shoot X-rays through the crystal, and the diffraction pattern elucidates the protein’s structure. Today, for the first time, a study in Science led by Crispr/Cas9 pioneer Jennifer Doudna uses that technique to capture the structure of activated Cas9, in the moment it’s primed to cut DNA.
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