DNA topoisomerases: enzymes that change the shape of DNA.

: The topological state of DNA plays a crucial role in many biological processes including DNA replication and gene expression. DNA topoisomerases are enzymes, present in all cells, that modulate and regulate the topology of DNA, e.g. by introducing or removing DNA supercoils. New insight into the reaction mechanisms and cellular functions of these biologically essential proteins has come from novel enzymatic and genetic approaches. Medical interest in topoisomerases has developed from the discovery that they are the intracellular targets for drugs used in the treatment of infectious diseases and cancer. This review describes mechanistic, biological and medical advances in our understanding of these intriguing proteins.