The core DNAs within the λ -int(75–356) synaptic complex (a, b), the λ -int post-strand exchange complex (d, e) and the λ -int Holliday junction complex (g, h) are shown along with schematic diagrams illustrating the inter-branch angles and position of branch points. The pair of λ -int subunits in the active conformation (orange) is positioned closer to the centre of each complex, whereas the inactive pair of subunits (cyan) is further apart. Scissile phosphates (spheres) activated for cleavage are coloured in red. A sharp kink in the bottom strand located two (c; synaptic) or four (f; post-exchange) nucleotides from the site of top strand cleavage is marked with arrows.