DNA SUPERCOILING DEPENDS ON THE PHOSPHORYLATION POTENTIAL IN ESCHERICHIA-COLI

ATP/ADP ratios were varied in different ways and the degree of negativ e supercoiling was determined in Escherichia coil. Independent of whet her the ATP/ADP ratio was reduced by a shift to anaerobic conditions, by addition of a protonophore (dinitrophenol) or by potassium cyanide addition, DNA supercoiling decreased similarly with the ATP/ADP ratio. The experiments were performed under well-defined conditions, where o xidative phosphorylation was the dominant route for ATP synthesis, i.e . using a minimal salts medium with succinate as the sole free-energy and carbon source, and in the presence or absence of ammonia as the ni trogen source. The results of the different experiments were consisten t with a single linear relationship between the log(ATP/ADP) and the c hange in linking number. The dependence of DNA supercoiling on the ATP /ADP ratio was not influenced by inhibitors of transcription or transl ation. Because the ATP/ADP ratio was modulated in different ways, the unique relationship suggests coupling between the phosphorylation pote ntial and DNA supercoiling. This was most probably mediated by the DNA gyrase, independent of topoisomerase I or transcription.