A topoisomerase II-dependent mechanism for resetting replicons at the S-M-phase transition.

Topoisomerase II (topo II) is required for chromosome segregation and for reprogramming replicons. Here, we show that topo II couples DNA replication termination with the clearing of replication complexes for resetting replicons at mitosis. Topo II inhibition impairs completion of DNA replication, accounting for replication protein A (RPA) stabilization onto ssDNA. Topo II inhibition does not affect the caffeine-sensitive ORC1 degradation found upon origin firing, but it impairs the cdk-dependent degradation/chromatin dissociation of an ORC1/2 reservoir at mitosis. Our results show that ORC1 degradation is rescued by Pin1 depletion and that this topo II-dependent clearing of ORC1/2 from chromatin involves the APC.