Genome-wide mapping of Topoisomerase I activity sites reveal its role in chromosome segregation

To understand genome-wide TopoI engagements in vivo, functional sites were mapped by employing a poisonous variant of the enzyme and a newly discovered inhibitor. Co-localization of binding and cleavage sites of the enzyme on transcription units imply that both TopoI recruitment and function are associated with active transcription. Notably, TopoI is inactive upstream of the TSS and activated following transcription initiation. The binding of TopoI at Ter region, and the DNA cleavage at Ter indicate TopoI involvement in chromosome segregation, substantiated by its catenation and decatenation activities.