Nucleic Acids Research Advance Access published online on September 25, 2006
Nucleic Acids Research, doi:10.1093/nar/gkl682
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© 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 |
Replication fork blockage by transcription factor-DNA complexes in Escherichia coli
School of Medical Sciences, Institute of Medical Sciences University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, UK 1 Department of Biochemistry, University of Oxford, South Parks Road Oxford OX1 3QU, UK
*To whom correspondence should be addressed. Tel: +44 0 1224 555183; Fax: +44 0 1224 555844; Email: p.mcglynn{at}abdn.ac.uk
Received August 23, 2006. Accepted September 5, 2006.
All organisms require mechanisms that resuscitate replication forks when they break down, reflecting the complex intracellular environments within which DNA replication occurs. Here we show that as few as three lac repressor-operator complexes block Escherichia coli replication forks in vitro regardless of the topological state of the DNA. Blockage with tandem repressor-operator complexes was also observed in vivo, demonstrating that replisomes have a limited ability to translocate through high affinity protein–DNA complexes. However, cells could tolerate tandem repressor-bound operators within the chromosome that were sufficient to block all forks in vitro. This discrepancy between in vitro and in vivo observations was at least partly explained by the ability of RecA, RecBCD and RecG to abrogate the effects of repressor-operator complexes on cell viability. However, neither RuvABC nor RecF were needed for normal cell growth in the face of such complexes. Holliday junction resolution by RuvABC and facilitated loading of RecA by RecF were not therefore critical for tolerance of protein–DNA blocks. We conclude that there is a trade-off between efficient genome duplication and other aspects of DNA metabolism such as transcriptional control, and that recombination enzymes, either directly or indirectly, provide the means to tolerate such conflicts.
The authors wish it to be known that, in their opinion, the first two authors should be regarded as joint First Authors
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