Discovery of potent and versatile CRISPR-Cas9 inhibitors engineered for chemically controllable genome editing.

Anti-CRISPR (Acr) proteins are encoded by many mobile genetic elements (MGEs) such as phages and plasmids to combat CRISPR-Cas adaptive immune systems employed by prokaryotes, which provide powerful tools for CRISPR-Cas-based applications. Here, we discovered nine distinct type II-A anti-CRISPR (AcrIIA24-32) families from Streptococcus MGEs and found that most Acrs can potently inhibit type II-A Cas9 orthologs from Streptococcus (SpyCas9, St1Cas9 or St3Cas9) in bacterial and human cells. Among these Acrs, AcrIIA26, AcrIIA27, AcrIIA30 and AcrIIA31 are able to block Cas9 binding to DNA, while AcrIIA24 abrogates DNA cleavage by Cas9. Notably, AcrIIA25.1 and AcrIIA32.1 can inhibit both DNA binding and DNA cleavage activities of SpyCas9, exhibiting unique anti-CRISPR characteristics. Importantly, we developed several chemically inducible anti-CRISPR variants based on AcrIIA25.1 and AcrIIA32.1 by comprising hybrids of Acr protein and the 4-hydroxytamoxifen-responsive intein, which enabled post-translational control of CRISPR-Cas9-mediated genome editing in human cells. Taken together, our work expands the diversity of type II-A anti-CRISPR families and the toolbox of Acr proteins for the chemically inducible control of Cas9-based applications.