FIGURE 2.

Biological roles for resolvases. (A) Some resolvases (e.g., γδ and Tn3) are encoded by replicative transposons. Their transposition creates a branched intermediate (center panel) that is processed by the host replication and repair machinery (new DNA strands are in blue) to yield a “cointegrate” (fourth panel) in which both the donor and recipient replicons are fused. Resolvase action at a res site within the transposon (yellow) resolves the co-integrate into the original donor and the recipient that now carries a copy of the transposon. (B) Some resolvases (e.g., β and Sin) are encoded by plasmids. Rescue of a stalled replication fork by a homologous recombination-mediated pathway can lead to a Holliday Junction (HJ) behind the rescued fork (second panel). Depending on which pair of strands is cut to resolve the Holliday Junction, replication results in two daughter circles (upper branch) or in a plasmid dimer (lower branch). Action of the plasmid-encoded resolvase at a res site (yellow) converts this dimer into two daughter circles. In both examples, the product circles are initially linked as catenanes (not shown for simplicity; see Figure 3) that are later separated by a host type II topoisomerase. doi:10.1128/microbiolspec.MDNA3-0045-2014.f2