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Originally published in Science Express on 18 December 2008
Science 23 January 2009:
Vol. 323. no. 5913, pp. 509 - 512
DOI: 10.1126/science.1164346
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Reports

Electron Cryomicroscopy of E. coli Reveals Filament Bundles Involved in Plasmid DNA Segregation

Jeanne Salje,*{dagger} Benoît Zuber, Jan Löwe

Bipolar elongation of filaments of the bacterial actin homolog ParM drives movement of newly replicated plasmid DNA to opposite poles of a bacterial cell. We used a combination of vitreous sectioning and electron cryotomography to study this DNA partitioning system directly in native, frozen cells. The diffraction patterns from overexpressed ParM bundles in electron cryotomographic reconstructions were used to unambiguously identify ParM filaments in Escherichia coli cells. Using a low–copy number plasmid encoding components required for partitioning, we observed small bundles of three to five intracellular ParM filaments that were situated close to the edge of the nucleoid. We propose that this may indicate the capture of plasmid DNA within the periphery of this loosely defined, chromosome-containing region.

Medical Research Council (MRC) Laboratory of Molecular Biology, Hills Road, Cambridge CB2 0QH, UK.

{dagger} Present address: Kyoto University, Department of Biophysics, Faculty of Science, Oiwake Kitashirakawa, Sakyo-Ku, Kyoto 606-8502, Japan.

* To whom correspondence should be addressed. E-mail: jsalje{at}mrc-lmb.cam.ac.uk

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Science. ISSN 0036-8075 (print), 1095-9203 (online)