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Nucleic Acids Research Advance Access published online on December 3, 2007
Nucleic Acids Research, doi:10.1093/nar/gkm672
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© 2007 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.

Molecular Biology

Escherichia coli low-copy-number plasmid R1 centromere parC forms a U-shaped complex with its binding protein ParR

C. Hoischen1, M. Bussiek2, J. Langowski2 and S. Diekmann1,*

1Molecular Biology, FLI, Leibniz-Institute for Age Research, Beutenbergstrasse 11, D-07745 Jena, Germany and 2Division Biophysics of Macromolecules, DKFZ, INF 580, D-69120 Heidelberg, Germany

*To whom correspondence should be addressed. Tel: +49 3641 65 6260; Fax: +49 3641 65 6261; Email: diekmann{at}fli-leibniz.de

Received June 21, 2007. Revised August 15, 2007. Accepted August 16, 2007.

The Escherichia coli low-copy-number plasmid R1 contains a segregation machinery composed of parC, ParR and parM. The R1 centromere-like site parC contains two separate sets of repeats. By atomic force microscopy (AFM) we show here that ParR molecules bind to each of the 5-fold repeated iterons separately with the intervening sequence unbound by ParR. The two ParR protein complexes on parC do not complex with each other. ParR binds with a stoichiometry of about one ParR dimer per each single iteron. The measured DNA fragment lengths agreed with B-form DNA and each of the two parC 5-fold interon DNA stretches adopts a linear path in its complex with ParR. However, the overall parC/ParR complex with both iteron repeats bound by ParR forms an overall U-shaped structure: the DNA folds back on itself nearly completely, including an angle of ~150°. Analysing linear DNA fragments, we never observed dimerized ParR complexes on one parC DNA molecule (intramolecular) nor a dimerization between ParR complexes bound to two different parC DNA molecules (intermolecular). This bacterial segrosome is compared to other bacterial segregation complexes. We speculate that partition complexes might have a similar overall structural organization and, at least in part, common functional properties.

Present address: M. Bussiek, Biophysical Engineering Group, University of Twente, PO Box 217, NL-7500AE Enschede, The Netherlands.

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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