An encodable cysteine-containing sequence of amino acids Phe-Cys-Pro-Phe (FCPF), also known as π-clamp, offers selective modification of specific positions within a protein. In a recent publication, Rodrigo et al. utilized such technology to modify Cas proteins, including Cas9, Cas12, and Cas13, and reported that these engineered Cas proteins with the FCPF amino acid sequence insertion could be recognized by perfluoroaromatics and degraded through proteolysis-targeting chimera (PROTAC), indicating a potential strategy to reduce off-target edits related to hyperactivity of Cas proteins in genome editing.

You could find more information here: https://www.genscript.com/learning-center/regulating-cas-proteins-a-chemical-toolbox-aiding-genome-editing.html