IV CRISPR-Cas system displays PAM-dependent interference to vectors without showing nuclease activity to the target

Type IV CRISPR-Cas systems are often identified in plasmids 15, suggests the distribution of this system is related to horizontal gene transfer (HGT), moreover type IV systems exhibit strong targeting preference to plasmid-borne protospacers, which may suggest type IV systems are involved in an inter-plasmid competition 14. Type IV systems often co-occur with other CRISPR-Cas systems indicating a potential cross-talk between CRISPR systems 14, for type IV-A systems could adopt Cas1 and Cas2 from an associated system for the acquisition of spacers. Previous studies have shown the maturation of crRNA by a Cas6 variant (Caf5) and the formation of CRISPR-ribonucleoprotein complexes of the type IV-A system of Aromatoleum aromaticum. Another study has revealed Anti-plasmid interference activity of a Pseudomonas aeruginosa type IV-A system 16,17. However, the absence of Cas3 infers the interference of type IV-A systems sever different biological function than other CRISPR-Cas systems. In this study, we demonstrate that a type IV CRISPR-Cas system displays PAM-dependent interference to vectors without showing nuclease activity to the target. Additionally, we infer that the system provides immunity against bacteriophages.