Newly engineered eSpCas9 enables the efficient targeted gene editing of established CRISPR systems with the benefit of reduced off-target effects. Point mutations in the chromosome-binding motif of SpCas9, as described by Slaymaker, et al., provide higher on-target fidelity without loss of cleavage efficiency.
 Rationally engineered Cas9 nucleases with improved specificity. Slaymaker, I.M., et al. Science 351, 84-8, (2015)