title: Cellular architecture mediates DivIVA ultrastructure and regulates min activity in Bacillus subtilis.
abstract: The assembly of the cell division machinery at midcell is a critical step of cytokinesis. Many rod-shaped bacteria position septa using nucleoid occlusion, which prevents division over the chromosome, and the Min system, which prevents division near the poles. Here we examined the in vivo assembly of the Bacillus subtilis MinCD targeting proteins DivIVA, a peripheral membrane protein that preferentially localizes to negatively curved membranes and resembles eukaryotic tropomyosins, and MinJ, which recruits MinCD to DivIVA. We used structured illumination microscopy to demonstrate that both DivIVA and MinJ localize as double rings that flank the septum and first appear early in septal biosynthesis. The subsequent recruitment of MinCD to these double rings would separate the Min proteins from their target, FtsZ, spatially regulating Min activity and allowing continued cell division. Curvature-based localization would also provide temporal regulation, since DivIVA and the Min proteins would localize to midcell after the onset of division. We use time-lapse microscopy and fluorescence recovery after photobleaching to demonstrate that DivIVA rings are highly stable and are constructed from newly synthesized DivIVA molecules. After cell division, DivIVA rings appear to collapse into patches at the rounded cell poles of separated cells, with little or no incorporation of newly synthesized subunits. Thus, changes in cell architecture mediate both the initial recruitment of DivIVA to sites of cell division and the subsequent collapse of these rings into patches (or rings of smaller diameter), while curvature-based localization of DivIVA spatially and temporally regulates Min activity.
  
  
  OBJECTIVE
  The Min systems of Escherichia coli and Bacillus subtilis both inhibit FtsZ assembly, but one key difference between these two species is that whereas the E. coli Min proteins localize to the poles, the B. subtilis proteins localize to nascent division sites by interaction with DivIVA and MinJ. It is unclear how MinC activity at midcell is regulated to prevent it from interfering with FtsZ engaged in medial cell division. We used superresolution microscopy to demonstrate that DivIVA and MinJ, which localize MinCD, assemble double rings that flank active division sites and septa. This curvature-based localization mechanism holds MinCD away from the FtsZ ring at midcell, and we propose that this spatial organization is the primary mechanism by which MinC activity is regulated to allow division at midcell. Curvature-based localization also conveys temporal regulation, since it ensures that MinC localizes after the onset of division.
authors: Laboratory of Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, USA.
authors: Prahathees
authors: P
authors: Eswaramoorthy
authors: Marcella L
authors: ML
authors: Erb
authors: James A
authors: JA
authors: Gregory
authors: Jared
authors: J
authors: Silverman
authors: Kit
authors: K
authors: Pogliano
authors: Joe
authors: J
authors: Pogliano
authors: Kumaran S
authors: KS
authors: Ramamurthi
mesh_terms: D001412:Bacillus subtilis / Q000737:chemistry / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002455:Cell Division; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D018797:Cell Cycle Proteins; D003598:Cytoskeletal Proteins; C104636:DivIVA protein, bacteria; C071525:FtsZ protein, Bacteria; C080466:MinC protein, Bacteria