title: The Slow Mobility of the ParA Partitioning Protein Underlies Its Steady-State Patterning in Caulobacter.
abstract: In bacteria, ParABS systems mediate intracellular transport of various cargos, including chromosomal regions in Caulobacter crescentus. Transport of the ParB/parS partition complex requires the DNA-binding activity of ParA, which transiently tethers the partition complex during translocation. In C. crescentus, the directionality of the transport is set up by a gradient of ParA whose concentration gradually increases from one end of the cell (old pole) to the other (new pole). Importantly, this ParA gradient is already observed before DNA replication and segregation are initiated when the partition complex is anchored at the old pole. How such micron-scale ParA pattern is established and maintained before the initiation of chromosome segregation has not been experimentally established. Although the stimulation of ParA ATPase activity by the localized ParB/parS partition complex is thought to be involved, this activity alone cannot quantitatively describe the ParA pattern observed inside cells. Instead, our experimental and theoretical study shows that the missing key component for achieving the experimentally observed steady-state ParA patterning is the slow mobility of ParA dimers (D ∼10(-3)μm(2)/s) due to intermittent DNA binding. Our model recapitulates the entire steady-state ParA distribution observed experimentally, including the shape of the gradient as well as ParA accumulation at the location of the partition complex. Stochastic simulations suggest that cell-to-cell variability in ParA pattern is due to the low ParA copy number in C. crescentus cells. The model also accounts for an apparent exclusion of ParA from regions with small spacing between partition complexes observed in filamentous cells. Collectively, our work demonstrates that in addition to its function in mediating transport, the conserved DNA-binding property of ParA has a critical function before DNA segregation by setting up a ParA pattern required for transport directionality.
authors.affiliation: Microbial Sciences Institute, Yale University, New Haven, Connecticut; Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut; Howard Hughes Medical Institute, Yale University, New Haven, Connecticut.
authors.forename: Ivan V
authors.initials: IV
authors.lastname: Surovtsev
authors.affiliation: Microbial Sciences Institute, Yale University, New Haven, Connecticut; Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut.
authors.forename: Hoong Chuin
authors.initials: HC
authors.lastname: Lim
authors.affiliation: Microbial Sciences Institute, Yale University, New Haven, Connecticut; Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut; Howard Hughes Medical Institute, Yale University, New Haven, Connecticut; Department of Microbial Pathogenesis, Yale School of Medicine, New Haven, Connecticut. Electronic address: christine.jacobs-wagner@yale.edu.
authors.forename: Christine
authors.initials: C
authors.lastname: Jacobs-Wagner
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000465:Algorithms; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D016935:Caulobacter crescentus / Q000235:genetics / Q000378:metabolism*; D020090:Chromosome Segregation / Q000502:physiology; D002876:Chromosomes, Bacterial / Q000378:metabolism; D003198:Computer Simulation; D004269:DNA, Bacterial / Q000378:metabolism*; D004058:Diffusion; D004926:Escherichia coli; D036681:Fluorescence Recovery After Photobleaching; D006868:Hydrolysis; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D055503:Protein Multimerization; D013269:Stochastic Processes
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D008164:Luminescent Proteins; C052883:chromosome partition proteins, bacterial; C054562:yellow fluorescent protein, Bacteria; D000255:Adenosine Triphosphate