Genome editing: The domestication of Cas9.

Abstract

The enzyme Cas9 is used in genome editing to cut selected DNA sequences, but it also creates breaks at off-target sites. Protein engineering has now been used to make Cas9 enzymes that have minimal off-target effects. See Article p.490 The CRISPR–Cas9 nucleases now widely used in gene editing can be readily customized, but can also induce substantial genome-wide off-target mutations at sequences that resemble the on-target site. Keith Joung and colleagues report a high-fidelity variant of Cas9 from Streptococcus pyogenes that shows on-target activities comparable to the wild-type enzyme, but with off-target events that are undetectable by genome-wide break capture and targeted sequencing methods.