Kim, Y. BillKomor, Alexis C.Levy, JonathanPacker, Michael S.Zhao, KevinLiu, David2017-11-212017Kim, Y. Bill, Alexis C. Komor, Jonathan M. Levy, Michael S. Packer, Kevin T. Zhao, and David R. Liu. 2017. “Increasing the genome-targeting scope and precision of base editing with engineered Cas9-cytidine deaminase fusions.” Nature biotechnology 35 (4): 371-376. doi:10.1038/nbt.3803. http://dx.doi.org/10.1038/nbt.3803.http://nrs.harvard.edu/urn-3:HUL.InstRepos:34375291Base editing is a recently developed approach to genome editing that uses a fusion protein containing a catalytically defective Streptococcus pyogenes Cas9, a cytidine deaminase, and an inhibitor of base excision repair to induce programmable, single-nucleotide changes in the DNA of living cells without generating double-strand DNA breaks, without requiring a donor DNA template, and without inducing an excess of stochastic insertions and deletions1. Here we report the development of five new C→T (or G→A) base editors that use natural and engineered Cas9 variants with different protospacer-adjacent motif (PAM) specificities to expand the number of sites that can be targeted by base editing by 2.5-fold. Additionally, we engineered new base editors containing mutated cytidine deaminase domains that narrow the width of the apparent editing window from approximately 5 nucleotides to as little as 1 to 2 nucleotides, enabling the discrimination of neighboring C nucleotides that would previously be edited with comparable efficiency, thereby doubling the number of disease-associated target Cs that can be corrected preferentially over nearby non-target Cs. Collectively, these developments substantially increase the targeting scope of base editing and establish the modular nature of base editors.en-USBase editinggenome editingCRISPRCas9protein engineeringgenetic diseasesingle-nucleotide polymorphismJournal Article2017-11-2110.1038/nbt.3803