Sarah Zhang, Wired.com, January 14, 2016. http://www.wired.com/2016/01/crispr-modification/
Despite the importance of Cas9, no one has observed exactly how Cas9 cleaves targeted DNA. Previous crystal structures place the nuclease cleavage domains too far away for DNA cleavage to occur. In a recent Science publication (http://science.sciencemag.org/content/early/2016/01/13/science.aad8282) Jennifer Doudna’s group solved the crystal structure of Cas9 primed to cut targeted DNA. This crystal structure may allow the engineering of more accurate Cas9 endonucleases.