Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) loci and CRISPR-associated proteins (Cas) defend bacteria and archaea from bacteriophages by specifically targeting viral nucleic acids. Among these defense mechanisms, type III CRISPR-Cas systems provide an additional layer of protection through a distinct signaling pathway. When the type III CRISPR-Cas interference complex recognizes a foreign transcript, the Cas10 subunit starts to synthesize cyclic oligoadenylates. These signaling molecules bind to the sensory domains of ancillary effector proteins, triggering the activation of their effector domains. Once activated, these effectors can degrade RNA or DNA, inhibit translation, or disrupt membrane integrity, thus preventing viral replication or killing infected cells [1], [2].
Recent systematic analyses of previously uncharacterized genes within CRISPR-Cas operons have identified a wider range of effector proteins [3] with predicted biochemical activities not previously linked to CRISPR-Cas immunity. However, the precise functions of these novel effectors in type III CRISPR-Cas immunity remain unknown. In this study, we present the initial studies on novel putative type III CRISPR-Cas effectors demonstrating their activity in the heterologous E. coli host.