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1: EMBO J. 2008 Aug 20;27(16):2230-8. Epub 2008 Jul 24.
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Bacterial actin: architecture of the ParMRC plasmid DNA partitioning complex.

Salje J, Löwe J.

Structural Studies, MRC Laboratory of Molecular Biology, Cambridge, UK.

The R1 plasmid employs ATP-driven polymerisation of the actin-like protein ParM to move newly replicated DNA to opposite poles of a bacterial cell. This process is essential for ensuring accurate segregation of the low-copy number plasmid and is the best characterised example of DNA partitioning in prokaryotes. In vivo, ParM only forms long filaments when capped at both ends by attachment to a centromere-like region parC, through a small DNA-binding protein ParR. Here, we present biochemical and electron microscopy data leading to a model for the mechanism by which ParR-parC complexes bind and stabilise elongating ParM filaments. We propose that the open ring formed by oligomeric ParR dimers with parC DNA wrapped around acts as a rigid clamp, which holds the end of elongating ParM filaments while allowing entry of new ATP-bound monomers. We propose a processive mechanism by which cycles of ATP hydrolysis in polymerising ParM drives movement of ParR-bound parC DNA. Importantly, our model predicts that each pair of plasmids will be driven apart in the cell by just a single double helical ParM filament.

PMID: 18650930 [PubMed - indexed for MEDLINE]

PMCID: PMC2519105 [Available on 08/20/09]