biologylair:

Model for the DNA binding and cleavage fragment of yeast topoisomerase II (blue/red spheres) bound to a separated DNA strand (green spheres). One protomer is shaded darker than the other to highlight the protein’s two subunits. A second DNA (viewed end-on, yellow sticks) is modeled into a large internal hole present in the enzyme. This figure represents a likely conformational and substrate-bound intermediate of this region of the topoisomerase during its duplex DNA passage reaction.