Alteration of Escherichia coli topoisomerase IV to novobiocin resistance.

DNA gyrase and topoisomerase IV (topo IV) are the two essential type II topoisomerases of Escherichia coli. Gyrase is responsible for maintaining negative supercoiling of the bacterial chromosome, whereas topo IV's primary role is in disentangling daughter chromosomes following DNA replication. Coumarins, such as novobiocin, are wide-spectrum antimicrobial agents that primarily interfere with DNA gyrase. In this work we designed an alteration in the ParE subunit of topo IV at a site homologous to that which confers coumarin resistance in gyrase. This parE mutation renders the encoded topo IV approximately 40-fold resistant to inhibition by novobiocin in vitro and imparts a similar resistance to inhibition of topo IV-mediated relaxation of supercoiled DNA in vivo. We conclude that topo IV is a secondary target of novobiocin and that it is very likely to be inhibited by the same mechanism as DNA gyrase.