Nucleic Acids Research Advance Access originally published online on December 6, 2006
Nucleic Acids Research 2007 35(1):79-86; doi:10.1093/nar/gkl981
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Nucleic Acids Research, 2007, Vol. 35, No. 1 79-86
© 2006 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Nucleic Acid Enzymes |
RecA can stimulate the relaxation activity of topoisomerase I: Molecular basis of topoisomerase-mediated genome-wide transcriptional responses in Escherichia coli
Department of Pharmacology, University of Minnesota Medical School-Twin Cities Minneapolis, MN 55455, USA 1 Department of Biochemistry, Molecular Biology & Biophysics and the Biotechnology Institute, University of Minnesota St Paul, MN 55108, USA
*To whom correspondence should be addressed at Hiroshi Hiasa, 6-120 Jackson Hall, 321 Church Street SE, Minneapolis, MN 55455, USA. Tel: +1 612 626 3101; Fax: +1 612 625 8408; Email: hiasa001{at}umn.edu
Received July 4, 2006. Revised August 23, 2006. Accepted October 28, 2006.
The superhelicity of the chromosome, which is controlled by DNA topoisomerases, modulates global gene expression. Investigations of transcriptional responses to the modulation of gyrase function have identified two types of topoisomerase-mediated transcriptional responses: (i) steady-state changes elicited by a mutation in gyrase, such as the D82G mutation in GyrA, and (ii) dynamic changes elicited by the inhibition of gyrase. We hypothesize that the steady-state effects are due to the changes in biochemical properties of gyrase, whereas the dynamic effects are due to an imbalance between supercoiling and relaxation activities, which appears to be influenced by the RecA activity. Herein, we present biochemical evidence for hypothesized mechanisms. GyrA D82G gyrase exhibits a reduced supercoiling activity. The RecA protein can influence the balance between supercoiling and relaxation activities either by interfering with the activity of DNA gyrase or by facilitating the relaxation reaction. RecA has no effect on the supercoiling activity of gyrase but stimulates the relaxation activity of topoisomerase I. This stimulation is specific and requires formation of an active RecA filament. These results suggest that the functional interaction between RecA and topoisomerase I is responsible for RecA-mediated modulation of the relaxation-dependent transcriptional activity of the Escherichia coli chromosome.
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