title: ParABS systems of the four replicons of Burkholderia cenocepacia: new chromosome centromeres confer partition specificity.
abstract: Most bacterial chromosomes carry an analogue of the parABS systems that govern plasmid partition, but their role in chromosome partition is ambiguous. parABS systems might be particularly important for orderly segregation of multipartite genomes, where their role may thus be easier to evaluate. We have characterized parABS systems in Burkholderia cenocepacia, whose genome comprises three chromosomes and one low-copy-number plasmid. A single parAB locus and a set of ParB-binding (parS) centromere sites are located near the origin of each replicon. ParA and ParB of the longest chromosome are phylogenetically similar to analogues in other multichromosome and monochromosome bacteria but are distinct from those of smaller chromosomes. The latter form subgroups that correspond to the taxa of their hosts, indicating evolution from plasmids. The parS sites on the smaller chromosomes and the plasmid are similar to the "universal" parS of the main chromosome but with a sequence specific to their replicon. In an Escherichia coli plasmid stabilization test, each parAB exhibits partition activity only with the parS of its own replicon. Hence, parABS function is based on the independent partition of individual chromosomes rather than on a single communal system or network of interacting systems. Stabilization by the smaller chromosome and plasmid systems was enhanced by mutation of parS sites and a promoter internal to their parAB operons, suggesting autoregulatory mechanisms. The small chromosome ParBs were found to silence transcription, a property relevant to autoregulation.
authors.affiliation: Laboratoire de Microbiologie et Génétique Moléculaire, Centre National de Recherche Scientifique, 118 route de Narbonne, 31062 Toulouse, France
authors.forename: Nelly
authors.initials: N
authors.lastname: Dubarry
authors.forename: Franck
authors.initials: F
authors.lastname: Pasta
authors.forename: David
authors.initials: D
authors.lastname: Lane
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000145:classification / Q000235:genetics*; D016956:Burkholderia cepacia / Q000235:genetics / Q000502:physiology*; D002455:Cell Division; D002503:Centromere; D020090:Chromosome Segregation; D002876:Chromosomes, Bacterial / Q000235:genetics* / Q000378:metabolism; D003851:Deoxyribonucleases / Q000235:genetics*; D016680:Genome, Bacterial / Q000502:physiology*; D008938:Mitosis; D008969:Molecular Sequence Data; D012093:Replicon / Q000235:genetics*; D016415:Sequence Alignment
chemical_list: D001426:Bacterial Proteins; C052883:chromosome partition proteins, bacterial; D003851:Deoxyribonucleases