Kim, Y.B. et al. Nat. Biotechnol. http://dx.doi.org/10.1038/nbt.3803 (2017).

The capabilities of the Cas9 nuclease can be tuned by the effector it is fused to. Nuclease active or inactive versions of Cas9 have been harnessed to transcriptional activators or repressors, to enzymes that modify epigenomic marks and, most recently, to a cytidine deaminase that changes cytidines to uridines and hence converts C:G base pairs to T:A. The base editors are elegant but have nonetheless faced several limitations: the strict PAM requirement of Streptococcus pyogenes and a five-base-pair editing window within which all cytosines are modified. Kim et al. make base editing more versatile by using Cas9 variants with different PAM specificities and by narrowing the editing window to one or two base pairs by introducing mutations into the deaminase that affect its binding to DNA.