Topoisomerase

Topoisomerases (type I: EC 5.99.1.2, type II: EC 5.99.1.3) are enzymes that regulate the overwinding or underwinding of DNA. The winding problem of DNA arises due to the intertwined nature of its double helical structure. For example, during DNA replication, DNA becomes overwound ahead of a replication fork. If left unabated, this tension would eventually grind replication to a halt (a similar event happens during transcription.)