Single-Molecule Study Of Site-Specific Dna Recombination By Gamma Delta Resolvase

γδ resolvase is a serine recombinase coded by γδ transposon, which catalyzes DNA recombination between two res sites (114 bp) on a negatively supercoiled circular DNA, resulting in two catenated DNA circles. Each res site contains 3 different resolvase binding sites - site I, II and III, and each binds to a resolvase dimer. We have developed a single-DNA based system whereby synapsis and recombination should lead to torsional relaxation of a single supercoiled DNA. DNA relaxation catalyzed by γδ resolvase occurs at much higher rate on DNA substrate containing 2 res sites than those containing 1 or 0 res site. Furthermore, reactions on a 2-res-site substrate show a characteristic ∼200 nm relaxation consistent with the +4 ΔLk observed to be associated with the recombination reaction in bulk experiments. We also have observed topoisomerase activity of γδ resolvase on the non-specific (0 res) DNA substrate.