DNA supercoiling by DNA gyrase |
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Authors: | Hans V Westerhoff Mary H O’Dea Anthony Maxwell Martin Gellert |
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Institution: | 1. Laboratory of Molecular Biology, National Institute of Diabetes, and Digestive and Kidney Diseases, National Institutes of Health, 20892, Bethesda, MD 2. Department of Biochemistry, University of Leicester, LE1 7RH, Leicester, UK
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Abstract: | Using purified DNA gyrase to supercoil circular plasmid pBR322 DNA, we examined how the linking number attained at the steady
state (‘static head’) varies with the concentrations of ATP and ADP, both in the absence and presence of spermidine. In the
absence of spermidine at total adenine nucleotide concentrations between 0.35 and 1.4 mM, the static-head linking number was independent of the sum concentration of ATP and ADP, but depended strongly on the ratio
of their concentrations. We established that the same linking number was attained independent of the direction from which
the steady state was approached. The decrease in linking number at static head is more extensive when spermidine is present
in the incubation, but remains a function of the ATP]-to-ADP] ratio.
These results are discussed in terms of various kinetic schemes for DNA gyrase. We present one kinetic scheme that accounts
for the experimental observations. According to this scheme our experimental results imply that there is significant slip
in DNA gyrase when spermidine is absent. It is possible that spermidine acts through adjustment of the degree of coupling
of DNA gyrase. |
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Keywords: | Index Entries" target="_blank">Index Entries Coupling slip supercoiled DNA linking number phosphate potential control free-energy transduction elasticity of DNA |
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