Journal
NATURE STRUCTURAL & MOLECULAR BIOLOGY
Volume 14, Issue 4, Pages 264-271Publisher
NATURE PUBLISHING GROUP
DOI: 10.1038/nsmb1213
Keywords
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Funding
- Biotechnology and Biological Sciences Research Council [BBS/E/J/00000201] Funding Source: Medline
- NIGMS NIH HHS [GM32543, GM31655] Funding Source: Medline
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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.
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