Model for Dpb11/TopBP1 function at anaphase bridges. During metaphase, the sister chromatids may be interlinked by hemicatenanes (A), Holliday junctions (B), catenanes (C), and unreplicated regions or termination zones (D). The hemicatenanes and unreplicated regions contain single-stranded DNA, which may act as a substrate to initiate homologous recombination (HR), leading to the formation of chromosomes connected by Holliday junctions. TopBP1-ATR inhibits recombination at replication forks and BLM-TopoIIIα promotes the nonrecombinogenic dissolution of hemicatenanes. Double-Holliday junctions can also be resolved by MUS81-EME1 or GEN1. During anaphase any remaining catenanes must be resolved by TopoII to prevent chromosome nondisjunction. The interaction of TopoII with TopBP1 may aid this process.