Fig. 3: The built-in signalling pathway of type III CRISPR–Cas systems.
From: An updated evolutionary classification of CRISPR–Cas systems including rare variants
a, Phylogenetic tree of Cas10 with information on associated genes involved in the signalling pathway and domain functionality mapped to the branches. Branches are colour-coded according to the key on the right. The circles around the tree show (from the inner to the outer): (1) inactive PALM (iPALM) domain, indicating that the respective Cas10 cannot make a second messenger molecule; (2) the presence of the HD-nuclease domain; (3)–(6) the presence of genes encoding Crf1, Crf2, Crf4 and Crf9 in the respective loci; (7) the presence of a gene encoding the CorA homologue; and (8) the presence of genes encoding SAM–AMP cleaving enzymes. b, Schematic of the signalling pathway. HEPN, PIN and RelE, ribonucleases of the respective families; CorA, divalent cation channel; HTH, helix-turn-helix domain. *In some Crf4 proteins, PD-(D/E)xK nuclease is capable of cleaving both DNA and RNA.
