TY - JOUR T1 - Lack of Cas13a inhibition by anti-CRISPR proteins from <em>Leptotrichia</em> prophages JF - bioRxiv DO - 10.1101/2021.05.27.445852 SP - 2021.05.27.445852 AU - Alexander J Meeske AU - Matthew C. Johnson AU - Logan T. Hille AU - Benjamin P. Kleinstiver AU - Joseph Bondy-Denomy Y1 - 2021/01/01 UR - http://biorxiv.org/content/early/2021/05/27/2021.05.27.445852.abstract N2 - CRISPR systems are prokaryotic adaptive immune systems that use RNA-guided Cas nucleases to recognize and destroy foreign genetic elements, like bacteriophages and plasmids. To overcome CRISPR immunity, phages have evolved diverse families of anti-CRISPR proteins (Acrs), each of which inhibits the nucleic acid binding or cleavage activities of specific Cas protein families. Recently, Lin et al. (2020) described the discovery and characterization of 7 different Acr families (AcrVIA1-7) that inhibit type VI-A CRISPR systems, which use the nuclease Cas13a to perform RNA-guided RNA cleavage. In this Matters Arising article, we detail several inconsistencies that question the results reported in the Lin et al. (2020) study. These include inaccurate bioinformatics analyses, as well as reported experiments involving bacterial strains that are impossible to construct. The authors were unable to provide their published strains with which we might reproduce their experiments. We independently tested the Acr sequences described in Lin et al. (2020) in two different Cas13 inhibition assays, but could not detect anti-CRISPR activity. Taken together, our data and analyses prompt us to question the claim that AcrVIA1-7 reported in Lin et al. are bona fide type VI anti-CRISPR proteins.Competing Interest StatementConflict of interest statement. J.B.-D. is a scientific advisory board member of SNIPR Biome and Excision Biotherapeutics and a scientific advisory board member and co-founder of Acrigen Biosciences. J.B.-D. is an inventor on patents filed by UCSF pertaining to anti-CRISPR technology. B.P.K is an inventor on patents and patent applications filed by Mass General Brigham that describe genome engineering technologies. B.P.K. consults for Avectas Inc., EcoR1 capital, and ElevateBio, and is an advisor to Acrigen Biosciences and Life Edit Therapeutics. ER -