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Updated: Mar 29, 2026

Using Sniper-Cas9 to Minimize Off-target Effects of CRISPR-Cas9 Without the Loss of On-target Activity Via Directed Evolution
Published on: February 26, 2019
Rationally engineered Cas9 nucleases with improved specificity
Ian M Slaymaker1, Linyi Gao2, Bernd Zetsche1
1Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA. McGovern Institute for Brain Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Abstract:
The RNA-guided endonuclease Cas9 is a versatile genome-editing tool with a broad range of applications from therapeutics to functional annotation of genes. Cas9 creates double-strand breaks (DSBs) at targeted genomic loci complementary to a short RNA guide. However, Cas9 can cleave off-target sites that are not fully complementary to the guide, which poses a major challenge for genome editing. Here, we use structure-guided protein engineering to improve the specificity of Streptococcus pyogenes Cas9 (SpCas9). Using targeted deep sequencing and unbiased whole-genome off-target analysis to assess Cas9-mediated DNA cleavage in human cells, we demonstrate that "enhanced specificity" SpCas9 (eSpCas9) variants reduce off-target effects and maintain robust on-target cleavage. Thus, eSpCas9 could be broadly useful for genome-editing applications requiring a high level of specificity.
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