title: Centromere pairing by a plasmid-encoded type I ParB protein.
abstract: The par2 locus of Escherichia coli plasmid pB171 encodes two trans-acting proteins, ParA and ParB, and two cis-acting sites, parC1 and parC2, to which ParB binds cooperatively. ParA is related to MinD and oscillates in helical structures and thereby positions ParB/parC-carrying plasmids regularly over the nucleoid. ParB ribbon-helix-helix dimers bind cooperatively to direct repeats in parC1 and parC2. Using four different assays we obtain solid evidence that ParB can pair parC1- and parC2-encoding DNA fragments in vitro. Convincingly, electron microscopy revealed that ParB mediates binary pairing of parC fragments. In addition to binary complexes, ParB mediated the formation of higher order complexes consisting of several DNA fragments joined by ParB at centromere site parC. N-terminal truncated versions of ParB still possessing specific DNA binding activity were incompetent in pairing, hence identifying the N terminus of ParB as a requirement for ParB-mediated centromere pairing. These observations suggest that centromere pairing is an important intermediate step in plasmid partitioning mediated by the common type I loci.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark.
authors.forename: Simon
authors.initials: S
authors.lastname: Ringgaard
authors.forename: Jan
authors.initials: J
authors.lastname: Löwe
authors.forename: Kenn
authors.initials: K
authors.lastname: Gerdes
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001483:Base Sequence; D002503:Centromere / Q000648:ultrastructure*; D004247:DNA / Q000737:chemistry; D019915:DNA Primase; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D004583:Electrons; D004706:Endodeoxyribonucleases / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000378:metabolism*; D005090:Exodeoxyribonucleases / Q000378:metabolism*; D008969:Molecular Sequence Data; D009991:Oscillometry; D010957:Plasmids / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D013050:Spectrometry, Fluorescence
chemical_list: D029968:Escherichia coli Proteins; D004247:DNA; D019915:DNA Primase; D004706:Endodeoxyribonucleases; D005090:Exodeoxyribonucleases; C121791:dnaG protein, E coli