COUMERMYCIN A1 - PREFERENTIAL INHIBITOR OF REPLICATIVE DNA-SYNTHESIS IN ESCHERICHIA-COLI .2. INVITRO CHARACTERIZATION

In vitro inhibitions by coumermycin A1 of DNA and RNA synthesis in toluenized cells were studied. In a sensitive strain, 50% inhibitions of replication and transcription were observed at 0.035 and 0.600 .mu.g/ml, respectively. DNA synthesis in a toluenized-resistant mutant was 50% inhibited at 0.140 .mu.g/ml of coumermycin A1; RNA synthesis was unaffected at all concentrations tested. Studies with a mixture of toluenized-sensitive and -resistant bacteria ruled out the presence of a diffusable activator or inhibitor of coumermycin A1 action. Density label studies with toluenized pol A+ and pol A- strains indicated that replicative DNA synthesis was specifically inhibited, in agreement with the in vivo studies in a preceding paper. Highly purified E. coli DNA polymerase III and RNA polymerase both were inhibited by this antibiotic. The high concentrations necessary for these inhibitions suggest that they are not biologically relevant. No interaction between DNA and coumermycin A1 was observed with the following analytical procedures: UV difference spectra, DNA absorbance-temperature transitions, equilibrium buoyant density centrifugation and DNA cross-linking determinations.