Interaction of the plasmid-encoded quinolone resistance protein QnrA with Escherichia coli topoisomerase IV.

Purified QnrA blocked ciprofloxacin inhibition of topoisomerase IV, just as QnrA was previously found to prevent quinolone inhibition of DNA gyrase. With a gel displacement assay, tagged QnrA was shown to bind to topoisomerase IV and its subunits in a reaction that did not depend on the presence of DNA, quinolone, or ATP.