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LF\n                    <jats:sub>N<\/jats:sub>\n                    -Acr\/PA is a nontoxic, two-component protein system derived from anthrax toxin, where protective antigen (PA) proteins bind receptors widespread in human cells, forming a pH-triggered endosomal pore that an engineered Acr (LF\n                    <jats:sub>N<\/jats:sub>\n                    -Acr) binds and uses to enter the cell. In the presence of PA, LF\n                    <jats:sub>N<\/jats:sub>\n                    -Acr enters human cells (e.g., immortalized cell lines, embryonic stem cells, and 3D cell cultures) at concentrations as low as 2.5 pM to inhibit up to 95% of Cas9-mediated knockout, knock-in, transcriptional activation, and base editing. Timing LF\n                    <jats:sub>N<\/jats:sub>\n                    -Acr delivery reduces off-target base editing and increases Cas9 specificity by 41%. LF\n                    <jats:sub>N<\/jats:sub>\n                    -Acr\/PA is the most potent known cell-permeable CRISPR-Cas inhibition system, significantly improving the utility of CRISPR for genome editing.\n                  <\/jats:p>","DOI":"10.1073\/pnas.2426960122","type":"journal-article","created":{"date-parts":[[2025,8,4]],"date-time":"2025-08-04T19:05:07Z","timestamp":1754334307000},"update-policy":"https:\/\/doi.org\/10.1073\/pnas.cm10313","source":"Crossref","is-referenced-by-count":8,"title":["Protective antigen\u2013mediated delivery of an anti-CRISPR protein for precision genome editing"],"prefix":"10.1073","volume":"122","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-4522-2793","authenticated-orcid":false,"given":"Axel O.","family":"Vera","sequence":"first","affiliation":[{"name":"Department of Chemistry, Massachusetts Institute of Technology","place":["Cambridge"]},{"name":"Chemical Biology and Therapeutics Science Program, Broad Institute of MIT and 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