Fig. 1: Type III CRISPR systems with a CorA effector.

a, A phylogenetic tree of Cas10 proteins from type III CRISPR systems of complete bacterial and archaeal genomes, colour coded by subtype⁴². Red bars on the outer ring indicate systems associated with a CorA-family effector protein. There are three main clusters of CorA-associated Cas10s, labelled CorA-1, CorA-2 and CorA-3. b, Genome context and effectors of selected type III-B CRISPR systems with a corA gene (cluster CorA-1: B. fragilis, Aliarcobacter butzleri, Methanococcus vannielii, Streptococcus oralis, Snytrophothermus lipocalidus, Clostridium botulinum). The type III-B cas genes cmr1–6 are shown in grey, with cas6 in purple and the adaptation genes cas1 (or a gene encoding a fused reverse transcriptase–Cas1 protein) and cas2 in green. The putative membrane channel protein is encoded by the corA gene (blue), which is adjacent to or fused with the genes encoding the PDEs NrN or DEDD (red). In C. botulinum, the PDE is replaced with a predicted SAM lyase. The wyl and nprR genes encode predicted transcriptional regulators. c, Plasmid challenge assay. E. coli BL21 Star cells expressing B. fragilis Cmr (wild-type or cyclase-defective variant) programmed with target (tetR) or non-target (pUC19) CRISPR RNA (crRNA) species were transformed with a pRAT plasmid that expressed the NrN and/or CorA proteins and carried a tetracycline resistance gene. Resistance was observed only when a targeting crRNA, active cyclase and both effector proteins were all present. Raw data are presented in Supplementary Data Fig. 1.