Folded chromosomes isolated from Escherichia coli strains after treatment with coumermycin A1in vivo, an inhibitor of DNA gyrase (Gellert et al., 1976a,b), were found to have reduced DNA superhelical densities. This loss of DNA supercoiling paralleled inhibition of DNA synthesis. Coumermycin also produced a loss of supercoiling in non-replicating chromosomes that had been synchronized by amino acid starvation. The drug had no effect on supercoiling in chromosomes isolated from a mutant bacterial strain from which Gellert et al. found coumermycin-resistant gyrase activity. Thus, the correlation between coumermycin inhibition of cell growth, DNA synthesis, and in vitro gyrase activity now extends to the loss of chromosomal DNA supercoiling. It appears that DNA gyrase may be responsible for the maintenance of negative supercoiling in the E. coli chromosome. Moreover, the chromosomal DNA remained intact after drug treatments, indicating that loss of supercoiling arises from the action of a DNA-relaxing activity.
All Science Journal Classification (ASJC) codes
- Structural Biology
- Molecular Biology