Topoisomerase:A class ofenzymesthat alter the supercoiling of double-strandedDNA. (Insupercoiling the DNAmoleculecoils up like a telephonecord, which shortens the molecule.) The topoisomerases act by transiently cutting one or both strands of the DNA.Topoisomerasetype I cuts one strand whereas topoisomerase type II cuts both strands of the DNA to relax the coil and extend the DNA molecule.
DNA超级的规定coiling isessentialto DNAtranscriptionandreplication, when the DNA helix must unwind to permit the proper function of the enzymatic machinery involved in these processes. Topoisomerases serve to maintain both the transcription and replication of DNA.
Aside from topoisomerases I and II, there are more discovered topoisomerases. Topoisomerase III may regulate复合while topoisomerase IV regulates theprocessof segregating newly replicatedchromosomesfrom one another.
