biostudies-literatureMeeske AJHoward Hughes Medical InstituteBurroughs Wellcome FundNIH Office of the DirectorNational Cancer InstituteNCI NIH HHSNational Institute of General Medical SciencesNIGMS NIH HHS54-59https://www.ebi.ac.uk/biostudies/studies/S-EPMC7975689biostudies-literatureUnknown369(6499)The CRISPR RNA (crRNA)-guided nuclease Cas13 recognizes complementary viral transcripts to trigger the degradation of both host and viral RNA during the type VI CRISPR-Cas antiviral response. However, how viruses can counteract this immunity is not known. We describe a listeriaphage (ϕLS46) encoding an anti-CRISPR protein (AcrVIA1) that inactivates the type VI-A CRISPR system of <i>Listeria seeligeri</i> Using genetics, biochemistry, and structural biology, we found that AcrVIA1 interacts with the guide-exposed face of Cas13a, preventing access to the target RNA and the conformational changes required for nuclease activation. Unlike inhibitors of DNA-cleaving Cas nucleases, which cause limited immunosuppression and require multiple infections to bypass CRISPR defenses, a single dose of AcrScience (New York, N.Y.)A phage-encoded anti-CRISPR enables complete evasion of type VI-A CRISPR-Cas immunity.PMC79756891DP1GM128184-01GM129430P30 CA008748P30CA008748DP1 GM128184R01 GM129430PATH AwardCassel AKKozlova ALiao JPatel DJJia NWiedmann MMeeske AJMarraffini LAfalseA phage-encoded anti-CRISPR enables complete evasion of type VI-A CRISPR-Cas immunity.The CRISPR RNA (crRNA)-guided nuclease Cas13 recognizes complementary viral transcripts to trigger the degradation of both host and viral RNA during the type VI CRISPR-Cas antiviral response. However, how viruses can counteract this immunity is not known. We describe a listeriaphage (ϕLS46) encoding an anti-CRISPR protein (AcrVIA1) that inactivates the type VI-A CRISPR system of <i>Listeria seeligeri</i> Using genetics, biochemistry, and structural biology, we found that AcrVIA1 interacts with the guide-exposed face of Cas13a, preventing access to the target RNA and the conformational changes required for nuclease activation. Unlike inhibitors of DNA-cleaving Cas nucleases, which cause limited immunosuppression and require multiple infections to bypass CRISPR defenses, a single dose of Acr2020-01-01T00:00:00Z2020 Jul2026-05-09T09:50:42.95Z2025-04-06T13:15:38.833ZS-EPMC79756893246733110.1126/science.abb6151