A multidomain hub anchors the chromosome segregation and chemotactic machinery to the bacterial pole.

Division of Infectious Diseases, Brigham and Women's Hospital.
Genes & development (Impact Factor: 12.64). 10/2012; 26(20):2348-60. DOI: 10.1101/gad.199869.112
Source: PubMed

ABSTRACT The cell poles constitute key subcellular domains that are often critical for motility, chemotaxis, and chromosome segregation in rod-shaped bacteria. However, in nearly all rods, the processes that underlie the formation, recognition, and perpetuation of the polar domains are largely unknown. Here, in Vibrio cholerae, we identified HubP (hub of the pole), a polar transmembrane protein conserved in all vibrios, that anchors three ParA-like ATPases to the cell poles and, through them, controls polar localization of the chromosome origin, the chemotactic machinery, and the flagellum. In the absence of HubP, oriCI is not targeted to the cell poles, chemotaxis is impaired, and a small but increased fraction of cells produces multiple, rather than single, flagella. Distinct cytoplasmic domains within HubP are required for polar targeting of the three ATPases, while a periplasmic portion of HubP is required for its localization. HubP partially relocalizes from the poles to the mid-cell prior to cell division, thereby enabling perpetuation of the polar domain in future daughter cells. Thus, a single polar hub is instrumental for establishing polar identity and organization.

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    ABSTRACT: The segregation of bacterial chromosomes follows a precise choreography of spatial organisation. It is initiated by the bipolar migration of the sister copies of the replication origin (ori). Most bacterial chromosomes contain a partition system (Par) with parS sites in close proximity to ori that contribute to the active mobilisation of the ori region towards the old pole. This is thought to result in a longitudinal chromosomal arrangement within the cell. In this study, we followed the duplication frequency and the cellular position of 19 Vibrio cholerae genome loci as a function of cell length. The genome of V. cholerae is divided between two chromosomes, chromosome I and II, which both contain a Par system. The ori region of chromosome I (oriI) is tethered to the old pole, whereas the ori region of chromosome II is found at midcell. Nevertheless, we found that both chromosomes adopted a longitudinal organisation. Chromosome I extended over the entire cell while chromosome II extended over the younger cell half. We further demonstrate that displacing parS sites away from the oriI region rotates the bulk of chromosome I. The only exception was the region where replication terminates, which still localised to the septum. However, the longitudinal arrangement of chromosome I persisted in Par mutants and, as was reported earlier, the ori region still localised towards the old pole. Finally, we show that the Par-independent longitudinal organisation and oriI polarity were perturbed by the introduction of a second origin. Taken together, these results suggest that the Par system is the major contributor to the longitudinal organisation of chromosome I but that the replication program also influences the arrangement of bacterial chromosomes.
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    ABSTRACT: P. aeruginosa ParA belongs to a large subfamily of Walker-type ATPases acting as partitioning proteins in bacteria. ParA has the ability to both self-associate and interact with its partner ParB. Analysis of the deletion mutants defined the part of the protein involved in dimerization and interactions with ParB. Here, a set of the ParA alanine substitution mutants in the region between E67 and L85 was created and analyzed in vivo and in vitro. All mutants impaired in dimerization (substitutions at positions M74, H79, Y82, L84) were also defective in interactions with ParB suggesting that ParA-ParB interactions depend on the ability of ParA to dimerize. Mutants with alanine substitutions at positions E67, C68, L70, E72, F76, Q83 and L85 were not impaired in dimerization but defective in interactions with ParB. The dimerization interface partly overlaps the pseudo-hairpin, involved in interactions with ParB. ParA mutant derivatives tested in vitro showed no defects in ATPase activity. Two parA alleles, parA84, whose product can neither self-interact nor interact with ParB, and parA67, whose product is impaired in interactions with ParB but not in dimerization, were introduced into P. aeruginosa chromosome by homologous gene exchange. Both mutants showed defective separation of ParB foci but to different extents. Only PAO1161 parA84 was visibly impaired in chromosome segregation, growth rate and motilities similarly to a parAnull mutant.
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