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September 2013 Volume 31 No 9

Heat maps of the specificity of DNA cleavage by RNA-guided Cas9 endonuclease. Four groups use a variety of methods in vitro and in cells to assess the specificity of genome editing with CRISPR-Cas systems (pp 822, 827, 833, 839). Credit: Marina Spence, based on images provided by David Liu, Prashant Mali and Feng Zhang.