DNA CLEAVAGE IS NOT REQUIRED FOR THE BINDING OF QUINOLONE DRUGS TO THE DNA GYRASE - DNA COMPLEX

The primary target for the quinolone group of antibacterial agents is DNA gyrase. One model for the interaction of quinolone drugs with gyra se and DNA suggests that the drugs bind to the single-stranded regions revealed following DNA cleavage by the enzyme. We have tested this hy pothesis by using mutants which have the active-site tyrosine in the g yrase A subunit altered to phenylalanine or serine. We have found that proteins bearing these mutations are still able to bind drug, suggest ing that DNA cleavage is not a prerequisite for drug binding. We have also found that the blocking of transcription by RNA polymerase in vit ro by the gyrase-quinolone complex on DNA does not occur when the acti ve-site tyrosine is mutated to serine; i.e., polymerase blocking requi res DNA cleavage.