Enhanced genome editing with a Streptococcus equinus Cas9

A large number of SpCas9 orthologs has been computationally identified, but their genome editing potential remains largely unknown. In this study, a GFP-activation assay was used to screen a panel of 18 SpCas9 orthologs, ten of which demonstrated activity in human cells. Notably, these orthologs had a preference for purine-rich PAM sequences. Four of the tested orthologs displayed enhanced specificity compared to SpCas9. Of particular interest is SeqCas9, which recognizes a simple NNG PAM and displays activity and specificity comparable to SpCas9-HF1. In addition, SeqCas9 exhibits superior base editing efficiency compared to SpCas9-NG and SpCas9-NRRH at multiple endogenous loci. This research sheds light on the diversity of SpCas9 orthologs and their potential for specific and efficient genome editing, especially in cases involving base editing.