Genome Editing Clustered regularly interspaced short palindromic repeats (CRISPR) function as part of an adaptive immune system in a range of prokaryotes: Invading phage and plasmid DNA is targeted for cleavage by complementary CRISPR RNAs (crRNAs) bound to a CRISPR-associated endonuclease (see the Perspective by van der Oost ). Cong et al. (p. 819 , published online 3 January) and Mali et al. (p. 823 , published online 3 January) adapted this defense system to function as a genome editing tool in eukaryotic cells.

RNA-Guided Human Genome Engineering via Cas9