Figure 2.

The architecture of CRISPR locus of VI CRISPR-Cas systems and their phylogenetic relationships. The class 2 systems (type VI CRISPR systems) consist of a single, comparatively larger Cas effector protein and CRISPR locus, which can be divided into four subtypes VI-A, VI-B1, VI-B2, VI-C, VI-D, VI-X, and VI-Y. Different colors represent different functional domains in this phylogenetic tree. The HEPN domains of each effector are represented by dark purple squares separated by other structural units. Grey rectangles denote CRISPR direct repeats (DRs), and dark purple squares indicate spacer sequences. The size of each effector and its corresponding conserved domain are indicated as the gene box.