Table 1.

Comparison of topoisomerases and site-specific recombinases

	TopIB	Tyrosine recombinases	Topo IA TopoII	Serine recombinases
Nucleophile	Y	Y	Y	S
Catalytic residues	RKR	RKR	E-(K), DxD, R	R, DRxxR
Metal ion	No	No	Mg2+	(Mg2+)
Cleavage product	3´-P-Tyr, 5´-OH	3´-P-Tyr, 5´-OH	5´-P-Tyr, 3´-OH	5´-P-Ser, 3´-OH
Multimer	monomer	tetramer	dimer, tetramer	tetramer
Mechanism	DNA swivel	swivel exchange	strand passage	strand passage?

* parentheses indicate what are applicable to certain but not all members.