Escherichia coli low-copy-number plasmid R1 centromere parC forms a U-shaped complex with its binding protein ParR.
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 approximately 150 degrees . 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.
Molecular Biology, FLI, Leibniz-Institute for Age Research, Beutenbergstrasse 11, D-07745 Jena, Germany.
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Hoischen
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Bussiek
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Langowski
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Diekmann
D001426:Bacterial Proteins / Q000378:metabolism* / Q000648:ultrastructure; D001665:Binding Sites; D002503:Centromere / Q000737:chemistry; D004269:DNA, Bacterial / Q000737:chemistry / Q000648:ultrastructure*; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins / Q000378:metabolism* / Q000648:ultrastructure; D018625:Microscopy, Atomic Force; D009690:Nucleic Acid Conformation; D010957:Plasmids / Q000235:genetics*; D012091:Repetitive Sequences, Nucleic Acid; D012097:Repressor Proteins / Q000378:metabolism* / Q000648:ultrastructure
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; C527285:ParR protein, E coli; C086169:ParR protein, bacteria; D012097:Repressor Proteins