Regulation of DNA Supercoiling in Escherichia coli

DNA supercoiling in Escherichia coli is an active process mediated by DNA gyrase. Intracellular DNA is kept under torsional stress (Sinden et al. 1980); mainte-nance of that stress, in the presence of DNA-relaxing topoisomerases, requires the continued activity of DNA gyrase. When DNA gyrase activity is blocked by inhib-itors or by mutational means, cellular DNA becomes at least partly relaxed (Drlica and Snyder 1978), and newly introduced DNA does not become supercoiled (Gellert et al. 1976b). The cellular functions of DNA are greatly affected by its supercoiling. If DNA gyrase activity is blocked, chromosomal replication and some forms of recombina-tion are halted, and the rate of transcription from some promoters is altered (for review, see Gellert 1981).