Novobiocin and coumermycin inhibit DNA supercoiling catalyzed by DNA gyrase.

Novobiocin and coumermycin are known to inhibit the replication of DNA iing of DNA catalyzed by E. coli DNA gyrase, a recently discovered enzyme that introduces negative superhelical turns into covalently circular DNA. The activity of DNA gyrase purified from a coumermycin-resistant mutant strain is resistant to both drugs. The inhibition by novobiocin of colicin E1 plasmid DNA replication in a cell-free system is partially relieved by adding resistant DNA gyrase. Both in the case of coliclls. DNA molecules which are converted to the covalently circular form in thepresence of coumermycin remain relaxed, instead of achieving their normal supercoiled conformation. We conclude that DNA gyrase controls the supercoiling of DNA in E. coli.