DNA TRANSPORT BY A TYPE-II TOPOISOMERASE - DIRECT EVIDENCE FOR A 2-GATE MECHANISM

Recent biochemical and crystallographic results suggest that a type II DNA topoisomerase acts as an ATP-modulated clamp with two sets of jaw s at opposite ends: a DNA-bound enzyme can admit a second DNA through one set of jaws; upon binding ATP, this DNA is passed through an enzym e-mediated opening in the first DNA and expelled from the enzyme throu gh the other set of jaws. Experiments based on the introduction of rev ersible disulfide links across one dimer interface of yeast DNA topois omerase II have confirmed this mechanism. The second DNA is found to e nter the enzyme through the gate formed by the N-terminal parts of the enzyme and leave it through the gate dose to the C termini.