Effects of transcription and translation on gyrase-mediated DNA cleavage in Escherichia coli

Gyrase-mediated DNA cleavage on plasmid DNAs was measured in Escherichia coli treated with oxolinic acid. On pBR322 DNA, gyrase cleavage sites were concentrated in the region between the 3′-ends of the tetA and bla genes. The preferential cleavage in this region was dependent on RNA transcription and the divergent orientation of these two transcription units. The enhanced gyrase cleavage also required translation; chloramphenicol treatment or the insertion of a translation terminator within the 5′-proximal region of the tetA gene abolished the enhanced cleavage. We suggest that the enhanced gyrase cleavage may reflect the changes in local DNA supercoiling during RNA transcription as gyrase cleavage in vitro was shown to be sensitive to the supercoiling state of DNA. The effects of transcription and translation on gyrase cleavage can best be explained by the twin-supercoiled-domain model of transcription (Liu, L. F., and Wang, J. C. (1987) Proc. Natl. Acad. Sci. U. S. A. 84, 7024-7027).