Figure 5.

Comparison of models of CRISPR spacer (left) and casposon (right) integration. The first nucleophilic attack occurs at the leader-repeat or the tRNA-TSD segment border by the 3′-OH end of the spacer or the casposon, respectively. After the formation of the half-site intermediate, the second nucleophilic attack occurs on the opposite strand at the repeat-spacer border (for CRISPR spacer) or at the junction between the TSD segment and the flanking DNA, distal to the tRNA gene (for casposon). The resulting single-stranded DNA gaps are repaired by uncharacterized mechanisms. The left panel has been modified from ref (19).