INVIVO ENHANCEMENT OF GENERAL AND SPECIFIC TRANSCRIPTION IN ESCHERICHIA-COLI BY DNA GYRASE ACTIVITY

The effect of drugs which inhibit DNA gyrase, including nalidixic acid, oxolinic acid and coumermycin, on transcription of Escherichia coli bacteria, phage and plasmid genomes was studied. Quantitative estimates of the synthesis of RNA under drug-treatment conditions showed that synthesis of many RNA species, including trp mRNA, was subject to inhibition by the drug. Transcription directed by the λ promoter pR was selectively less sensitive to the drug action than transcription initiated at the λ promoter pL. Evidence was obtained showing that diminished transcription resulted from less frequent RNA chain initiation rather than a premature arrest of the chain elongation. Inhibition of transcription by these DNA gyrase inhibitors was observed even in the absence of DNA replication. The inhibition by oxolinic acid or coumermycin was not observed in an E. coli strain bearing a nalAr mutation of a cour mutation, respectively. The reduction of trp mRNA synthesis in oxolinic acid-treated cells cannot be attributed to the increase in the rate of nascent mRNA degradation. These results indicate that DNA gyrase is generally required for intracellular RNA synthesis, and suggest that the supercolling of DNA by this winding enzyme enhances the initiation of transcription. © 1979.