Figure 3.

A proximity model for the regulation of topoisomerase II reactions by cohesin. Topoisomerase II undergoes bidirectional reactions, promoting both the resolution and re-catenation of DNA molecules. The cohesin complex (in orange) binds together two DNA molecules (in light blue and dark blue respectively), bringing them in close proximity. Such closeness can increase the chances of topoisomerase II-driven catenation of those strands, and thereby shifts the equilibrium towards the catenated state. Removal of cohesin results in physical separation of DNA molecules, rendering them unlikely to re-entangle once topoisomerase II separates them. Thus, upon cohesin removal, the equilibrium shifts, favoring sister chromatid resolution.