Inhibition of deoxyribonucleic acid gyrase: Effects on nucleic acid synthesis and cell division in Escherichia coli K-12

Abstract

Mutants of E. coli resistant to the antibiotic clorobiocin are also coumermycin resistant and the mutation to resistance in at least one mutant was mapped near gyrB. It is concluded, therefore, that clorobiocin inhibits DNA gyrase, and the drug was used to probe the role of this enzyme in vivo. DNA synthesis was preferentially inhibited but not completely blocked by the antibiotic. Transcription and cell division were also markedly affected. However, unlike other inhibitors of DNA synthesis, clorobiocin failed to induce the synthesis of protein X, the recA gene product. In mutants resistant to clorbiocin the replication velocity was unaffected, but initiation of DNA synthesis appeared to be delayed. It is concluded that DNA gyrase, and hence the supercoiled structure of the chromosome, is important for transcription, normal initiation of DNA replication, and cell division. The possible role of DNA gyrase in the elongation of replication forks is also discussed.