Topoisomerase I Structure and Mechanism

Sloan-Kettering - Molecular Biology: Stewart Shuman: "The eukaryotic type IB topoisomerase family includes nuclear topo I and the topoisomerases encoded by vaccinia and other cytoplasmic poxviruses. These enzymes relax DNA supercoils by transiently breaking and rejoining 1 strand of the DNA duplex. They act via a common mechanism, involving a covalent DNA-(3'-phosphotyrosyl)-topo intermediate. The participation of type IB topoisomerases in DNA replication, genetic recombination, and transcription, plus the fact that nuclear topo I is the target of the camptothecin anti-tumor drugs, mandates a thorough understanding of their mechanism of action."