Streptococcus uberis Cas9-A Compact Type II-A Nuclease Recognizing a Unique PAM and Functional in Human Cells.

Several type II Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-Cas9 RNA-guided nucleases are commonly used for genome engineering. Their relatively large size and requirements for specific protospacer adjacent motif (PAM) sequences flanking their targets prompt continuous searches for additional more compact Cas9 enzymes with new PAM specificities. Here, we present SuCas9, a compact nuclease from Streptococcus uberis, a bacterium inhabiting the mammary glands of dairy cattle. SuCas9 recognizes a novel 5'-NNAAA-3' PAM, efficiently cleaves DNA in vitro, and is active in human cells. SuCas9 thus expands the available genome editing toolset and may find biotechnological and medicinal applications in the future.