Purification of DNA Topoisomerases and Inhibition by Fluoroquinolones

Fluoroquinolones act by inhibiting the essential type II topoisomerases, DNA gyrase and topoisomerase IV (1 ). DNA gyrase is a tetramer composed of 2 A subunits and 2 B-subunits encoded for by gyrA and gyrB , respectively. This enzyme is the only enzyme known that is capable of negatively supercoiling DNA (2 ), a process essential for the bacterium to contain its DNA within the confines of the cell. Topoisomerase IV is also a tetramer composed of 2 C subunits and 2-E subunits encoded for by the parC and parE genes. This enzyme is involved in the unlinking of daughter chromosomes following replication (3 ).