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  • Title: Roles of topoisomerases in maintaining steady-state DNA supercoiling in Escherichia coli.
    Author: Zechiedrich EL, Khodursky AB, Bachellier S, Schneider R, Chen D, Lilley DM, Cozzarelli NR.
    Journal: J Biol Chem; 2000 Mar 17; 275(11):8103-13. PubMed ID: 10713132.
    Abstract:
    DNA supercoiling is essential for bacterial cell survival. We demonstrated that DNA topoisomerase IV, acting in concert with topoisomerase I and gyrase, makes an important contribution to the steady-state level of supercoiling in Escherichia coli. Following inhibition of gyrase, topoisomerase IV alone relaxed plasmid DNA to a final supercoiling density (sigma) of -0.015 at an initial rate of 0.8 links min(-1). Topoisomerase I relaxed DNA at a faster rate, 5 links min(-1), but only to a sigma of -0.05. Inhibition of topoisomerase IV in wild-type cells increased supercoiling to approximately the same level as in a mutant lacking topoisomerase I activity (to sigma = -0.08). The role of topoisomerase IV was revealed by two functional assays. Removal of both topoisomerase I and topoisomerase IV caused the DNA to become hyper-negatively supercoiled (sigma = -0.09), greatly stimulating transcription from the supercoiling sensitive leu-500 promoter and increasing the number of supercoils trapped by lambda integrase site-specific recombination.
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