Fig. 1.

Site-specific recombination mediated by Tn3 resolvase. (A) Site-specific recombination reactions. A DNA segment containing a sequence of interest (arrow) may be excised by breaking and rejoining the DNA within two sites (boxes) recognized by a recombinase. (If the substrate is circular, this reaction is sometimes called resolution.) Similarly, the segment can be inserted by the intermolecular, reverse reaction. Another alternative, inversion of the orientation of the DNA segment between the sites, is not shown. (B) Crystal structure ofγδ resolvase dimer bound to a 34-bp DNA fragment containing res site I (10). The protein backbone is shown, with the N-terminal, catalytic domains in yellow, the C-terminal, DNA-binding domains in green, and the interdomain linkers in orange. The DNA is in gray spacefill representation. (C) Cartoon representation of the structure shown in B, using the same color scheme. The chimeric Z-resolvases described here have Zif268 DNA-binding domains in place of the resolvase C-terminal domains (DBD), and a mutant version of the catalytic domain (CAT). The Z-sites have motifs recognized by Zif268 in place of the motifs recognized by the resolvase C-terminal domain (indicated by arrows).