AcrVIA6 Is a Monomeric DNA-Binding Protein That Does Not Directly Inhibit Cas13a.

The CRISPR-Cas system is a crucial adaptive immune mechanism in prokaryotes, providing defense against invading genetic elements. Among various CRISPR-Cas systems, the type VI-A system, employing RNA-guided RNase Cas13a, has been extensively studied for its ability to target and degrade single-stranded RNA. Anti-CRISPR (Acr) proteins have evolved as natural inhibitors of these systems, with AcrVIA proteins specifically targeting the Cas13a enzyme. However, there is currently conflicting debate regarding the anti-CRISPR function of AcrVIA6. This study reveals that AcrVIA6 functions as a DNA-binding protein rather than a Cas13a inhibitor, as it does not block RNA cleavage. These findings challenge its role in CRISPR-Cas regulation.