title: Multiple modes of Escherichia coli DNA gyrase activity revealed by force and torque.
abstract: E. coli DNA gyrase uses the energy of ATP hydrolysis to introduce essential negative supercoils into the genome, thereby working against the mechanical stresses that accumulate in supercoiled DNA. Using a magnetic-tweezers assay, we demonstrate that small changes in force and torque can switch gyrase among three distinct modes of activity. Under low mechanical stress, gyrase introduces negative supercoils by a mechanism that depends on DNA wrapping. Elevated tension or positive torque suppresses DNA wrapping, revealing a second mode of activity that resembles the activity of topoisomerase IV. This 'distal T-segment capture' mode results in active relaxation of left-handed braids and positive supercoils. A third mode is responsible for the ATP-independent relaxation of negative supercoils. We present a branched kinetic model that quantitatively accounts for all of our single-molecule results and agrees with existing biochemical data.
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, California 94720, USA.
authors.forename: Marcelo
authors.initials: M
authors.lastname: Nöllmann
authors.forename: Michael D
authors.initials: MD
authors.lastname: Stone
authors.forename: Zev
authors.initials: Z
authors.lastname: Bryant
authors.forename: Jeff
authors.initials: J
authors.lastname: Gore
authors.forename: Nancy J
authors.initials: NJ
authors.lastname: Crisona
authors.forename: Seok-Cheol
authors.initials: SC
authors.lastname: Hong
authors.forename: Sylvain
authors.initials: S
authors.lastname: Mitelheiser
authors.forename: Anthony
authors.initials: A
authors.lastname: Maxwell
authors.forename: Carlos
authors.initials: C
authors.lastname: Bustamante
authors.forename: Nicholas R
authors.initials: NR
authors.lastname: Cozzarelli
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D027081:DNA Gyrase / Q000378:metabolism*; D004269:DNA, Bacterial / Q000737:chemistry; D004278:DNA, Superhelical / Q000737:chemistry; D004926:Escherichia coli / Q000201:enzymology*; D008280:Magnetics; D008954:Models, Biological; D009690:Nucleic Acid Conformation / Q000187:drug effects; D021122:Protein Subunits / Q000378:metabolism; D019415:Torque
chemical_list: D004269:DNA, Bacterial; D004278:DNA, Superhelical; D021122:Protein Subunits; D000255:Adenosine Triphosphate; D027081:DNA Gyrase