. Author manuscript; available in PMC: 2014 Jan 18.

Published in final edited form as: ACS Chem Biol. 2013 Jan 4;8(1):82–95. doi: 10.1021/cb300648v

Table 1.

Classification of topoisomerases

Type	Polarity	Mechanism	Humans			Bacteria

			Genes	Proteins	Drugs	Genes	Proteins	Drugs
IA	5'-PY	Strand passage	TOP3A	Top3α	none	TOPA	Topo I	none
IA	5'-PY	Strand passage	TOP3B	Top3β	none	TOPB	Topo III	none

IB	3'-PY	Rotation	TOP1	Top1	anticancer	usually
IB	3'-PY	Rotation	TOP1MT	Top1mt	none (?)	none

						GYRA	Gyrase
			TOP2A	Top2α		GYRB	Gyrase
IIA	5'-PY	Strand passage			anticancer			Antibiotics
		ATPase	TOP2B	Top2β		PARC	Topo IV
						PARE	Topo IV

Type I enzymes are monomeric and cleave one strand of DNA for catalysis. Type II enzymes are homodimeric (humans) or heterotetrameric (bacteria), and cleave both strands of duplex DNA with a 5’-four-base overhang (see Fig. 2).