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J Biol Chem. 2008 Oct 17;283(42):28081-6. doi: 10.1074/jbc.M803833200. Epub 2008 Jul 24.

Protein-nanocrystal conjugates support a single filament polymerization model in R1 plasmid segregation.

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1
Department of Chemistry, University of California, Berkeley, California 94720, USA.

Abstract

To ensure inheritance by daughter cells, many low-copy number bacterial plasmids, including the R1 drug-resistance plasmid, encode their own DNA segregation systems. The par operon of plasmid R1 directs construction of a simple spindle structure that converts free energy of polymerization of an actin-like protein, ParM, into work required to move sister plasmids to opposite poles of rod-shaped cells. The structures of individual components have been solved, but little is known about the ultrastructure of the R1 spindle. To determine the number of ParM filaments in a minimal R1 spindle, we used DNA-gold nanocrystal conjugates as mimics of the R1 plasmid. We found that each end of a single polar ParM filament binds to a single ParR/parC-gold complex, consistent with the idea that ParM filaments bind in the hollow core of the ParR/parC ring complex. Our results further suggest that multifilament spindles observed in vivo are associated with clusters of plasmids segregating as a unit.

PMID:
18658133
PMCID:
PMC2568930
DOI:
10.1074/jbc.M803833200
[Indexed for MEDLINE]
Free PMC Article
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