Source:http://linkedlifedata.com/resource/umls/id/C1336767
NCI: Enzymes that change the degree of supercoiling in DNA by cutting one or both strands. Type I topoisomerases cut only one strand of DNA; type I topoisomerase of E. coli (omega protein) relaxes negatively supercoiled DNA and does not act on positively supercoiled DNA. Type II topoisomerases cut both strands of DNA; type II topoisomerase of E. coli (DNA gyrase) increases the degree of negative supercoiling in DNA and requires ATP. It is inhibited by several antibiotics, including nalidixic acid and ovobiocin. (The Dictionary of Cell Biology, 2nd ed., http://www.mblab.gla.ac.uk/~julian/dict.html)