Fig. 3

The CASTs: recruitment of CRISPR systems by Tn7-like and Mu-like transposons for RNA-guided transposition. A Organization of CAST-encoding Tn7-like and Mu-like transposons. Tns and tni genes encoded transposase subunits. Att, transposons attachment sites; HTH, helix-turn-helix DNA-binding protein; LE, RE, transposon left end and right end, respectively; DR, direct repeat. The designations are as in Fig. 1, but the genes are shown not to scale. Crossed block arrows denote inactivated enzymes. B Schematic depiction of the structures and functionalities of two distinct CASTs. PAM, protospacer-adjacent motifs. C The two alternative routes of CAST insertion. Genetic organization of the I-B CAST is shown. Underneath, on the left, is a schematic depiction of homing to the attachment site via TniQ, and on the right, a schematic depiction of RNA-guided transposition via TnsD root (on the right). At the bottom, are schematics of the new Tn7-carrying loci emerging as the result of the transposon insertion. LE, RE, transposon Left End and Right END, respectively