In response to the efficient attacks of the host CRISPR-Cas system, bacteriophages have evolved various resistance strategies, including encoding anti-CRISPR (Acr) proteins. Since their initial discovery in 2013, over a hundred Acr proteins have been identified. These proteins use different mechanisms to inhibit the recognition and cleavage of target nucleic acids by the Cas protein-RNA complex, and have great potential for development as gene editing regulatory elements.
