Recently determined crystal structures of several members of the λ integrase family of site-specific recombinases have provided insights into the cis versus trans action of active site constituents, and the processes of synapsis and strand exchange.
Grindley, N. D. F. (1997, October 1). Site-specific recombination: Synapsis and strand exchange revealed. Current Biology. Cell Press. https://doi.org/10.1016/s0960-9822(06)00314-9