Genome-wide target specificities of CRISPR RNA-guided programmable deaminases
- Kim, Daesik; Lim, Kayeong; Kim, Sang-Tae; Yoon, Sun-heui; Kim, Kyoungmi; Ryu, Seuk-Min; Kim, Jin-Soo
- Issue Date
- Nature Biotechnology, Vol.35 No.5, pp.475-480
- Cas9-linked deaminases, also called base editors, enable targeted mutation of single nucleotides in eukaryotic genomes. However, their off-target activity is largely unknown. Here we modify digested-genome sequencing (Digenome-seq) to assess the specificity of a programmable deaminase composed of a Cas9 nickase (nCas9) and the deaminase APOBEC1 in the human genome. Genomic DNA is treated with the base editor and a mixture of DNA-modifying enzymes in vitro to produce DNA double-strand breaks (DSBs) at uracil-containing sites. Off-target sites are then computationally identified from whole genome sequencing data. Testing seven different single guide RNAs (sgRNAs), we find that the rAPOBEC1-nCas9 base editor is highly specific, inducing cytosine-to-uracil conversions at only 18 +/- 9 sites in the human genome for each sgRNA. Digenome-seq is sensitive enough to capture off-target sites with a substitution frequency of 0.1%. Notably, off-target sites of the base editors are often different from those of Cas9 alone, calling for independent assessment of their genome-wide specificities.
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