Microcin B17 is a peptide antibiotic that inhibits DNA replication in Escherichia coli by targeting DNA gyrase. Previously, two independently isolated microcin B17-resistant mutants were shown to harbor the same gyrB point mutation that results in the replacement of tryptophan 751 by arginine in the GyrB polypeptide. We used site-directed mutagenesis to construct mutants in which tryptophan 751...

The mechanism of action of the quinolone analogs ofloxacin and S-25930, which are unusual because of the presence of a third ring with an asymmetric carbon, was studied. Drug-resistant strains of Escherichia coli were selected by serial passage in the presence of ofloxacin, and a mutation was mapped near the gyrA gene of DNA gyrase. DNA gyrase containing the A subunit purified from this strain ...

Reverse gyrase is the only topoisomerase that can introduce positive supercoils into DNA in an ATP-dependent process. It has a modular structure and harnesses a helicase-like domain to support a topoisomerase activity, thereby creating the unique function of positive DNA supercoiling. The isolated topoisomerase domain can relax negatively supercoiled DNA, an activity that is suppressed in rever...

Clerocidin (CL), a microbial diterpenoid, reacts with DNA via its epoxide group and stimulates DNA cleavage by type II DNA topoisomerases. The molecular basis of CL action is poorly understood. We establish by genetic means that CL targets DNA gyrase in the gram-positive bacterium Streptococcus pneumoniae, and promotes gyrase-dependent single- and double-stranded DNA cleavage in vitro. CL-stimu...

The DNA gyrase inhibitor novobiocin specifically inhibits the transcription of ribosomal RNA in vivo while protein synthesis and the mRNA transcription are only partly affected. In vitro the novobiocin inhibition is only observed when protein fraction, which stimulates ribosomal RNA synthesis, is present. These results indicate that DNA gyrase is involved in the transcription of ribosomal RNA, ...

Transcription of highly expressed genes has been shown to occur in stochastic bursts. But the origin of such ubiquitous phenomenon has not been understood. Here, we present the mechanism in bacteria. We developed a high-throughput, in vitro, single-molecule assay to follow transcription on individual DNA templates in real time. We showed that positive supercoiling buildup on a DNA segment by tr...

In order to study the interactions between Escherichia coli DNA gyrase and the gyrase interacting protein QnrB in vivo, we constructed a gyrB-gyrA fusion and validated its ability to correct the temperature-sensitive growth of gyrA and gyrB mutants. Like wild-type gyrA, the gyrB-gyrA fusion complemented a quinolone-resistant gyrA mutant to increase susceptibility. It functioned as an active typ...

Streptomyces filipinensis NR 0484 produced a new DNA gyrase inhibitor, cyclothialidine. It showed potent activity against DNA gyrases from Escherichia coli and Micrococcus luteus.

DNA gyrase has been purified to near homogeneity from Escherichia coli. The enzyme consists of two subunits of molecular weights 90,000 and 100,000 present in roughly equimolar amounts. The subunits can be identified as the products of two genes, determining resistance to coumermycin A1 and novobiocin (cou) and to nalidixic acid and oxolinic acid (nalA), respectively. These antibiotics were pre...

Coumermycin A1 is an inhibitor of DNA gyrase, an enzyme that catalyzes supercoiling of DNA and is required for bacterial DNA replication. We have investigated the activity of this coumarin antibiotic on Borrelia burgdorferi, a spirochete and the causative agent of Lyme disease. B. burgdorferi was more susceptible than many other eubacteria to coumermycin as well as novobiocin, another coumarin ...