DNA Topoisomerases: Type I

Abstract

Type I DNA topoisomerases change DNA supercoiling by introducing a transient single-strand break into duplex DNA in a reaction that involves the formation of a covalent intermediate between the enzyme and the broken strand. While most type I enzymes relax either negative supercoils or both negative and positive supercoils, the reverse gyrase found in hyperthermophilic eubacteria and archaea introduces positive supercoils into DNA at the expense of ATP hydrolysis. In eubacteria and archaea, type I topoisomerases collaborate with enzymes that generate DNA supercoiling to set the final supercoiling level of the chromosomal DNA. In all cell types, the type I topoisomerases are important for removing the negative and positive supercoiling generated by transcription and replication.