title: Bacterial actin: architecture of the ParMRC plasmid DNA partitioning complex.
abstract: 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.
authors.affiliation: Structural Studies, MRC Laboratory of Molecular Biology, Cambridge, UK.
authors.forename: Jeanne
authors.initials: J
authors.lastname: Salje
authors.forename: Jan
authors.initials: J
authors.lastname: Löwe
mesh_terms: D000199:Actins / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D027101:DNA Topoisomerase IV / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D004269:DNA, Bacterial / Q000378:metabolism* / Q000648:ultrastructure; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry; D010957:Plasmids / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D017433:Protein Structure, Secondary
chemical_list: D000199:Actins; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; C471255:ParM protein, E coli; C527285:ParR protein, E coli; D010455:Peptides; D027101:DNA Topoisomerase IV