The first topoisomerase, E. coli topo I, was discovered by James C. Wang.
Like all quinolones, it functions by inhibiting the two type II topoisomerase enzymes, namely DNA gyrase and topoisomerase IV.
Nalidixic acid and related antibiotics inhibit a subunit of DNA gyrase and topoisomerase IV and induce formation of cleavage complexes.
Topoisomerase-I is a nuclear enzyme that relieves torsional strain in DNA by opening single strand breaks.