A great study from the Zhang lab developing and comparing different novel Cas9 variants

https://pubmed.ncbi.nlm.nih.gov/32187529 

Mol Cel. 2020 May 21;78(4):794-800.e8. Epub 2020 Mar 17.

Highly Parallel Profiling of Cas9 Variant Specificity

Jonathan L Schmid-Burgk, Linyi Gao, David Li, Zachary Gardner, Jonathan Strecker, Blake Lash, Feng Zhang

Abstract
Determining the off-target cleavage profile of programmable nucleases is an important consideration for any genome editing experiment, and a number of Cas9 variants have been reported that improve specificity. We describe here tagmentation-based tag integration site sequencing (TTISS), an efficient, scalable method for analyzing double-strand breaks (DSBs) that we apply in parallel to eight Cas9 variants across 59 targets. Additionally, we generated thousands of other Cas9 variants and screened for variants with enhanced specificity and activity, identifying LZ3 Cas9, a high specificity variant with a unique +1 insertion profile. This comprehensive comparison reveals a general trade-off between Cas9 activity and specificity and provides information about the frequency of generation of +1 insertions, which has implications for correcting frameshift mutations.

Keywords: CRISPR-Cas9; Cas9 specificity variants; double-strand break detection; off-target analysis; tagmentation.