title: Dynamic localization of the cyanobacterial circadian clock proteins.
abstract: BACKGROUND
  The cyanobacterial circadian clock system has been extensively studied, and the structures, interactions, and biochemical activities of the central oscillator proteins (KaiA, KaiB, and KaiC) have been well elucidated. Despite this rich repository of information, little is known about the distribution of these proteins within the cell.
  
  
  RESULTS
  Here we report that KaiA and KaiC localize as discrete foci near a single pole of cells in a clock-dependent fashion, with enhanced polar localization observed at night. KaiA localization is dependent on KaiC; consistent with this notion, KaiA and KaiC colocalize with each other, as well as with CikA, a key input and output factor previously reported to display unipolar localization. The molecular mechanism that localizes KaiC to the poles is conserved in Escherichia coli, another Gram-negative rod-shaped bacterium, suggesting that KaiC localization is not dependent on other clock- or cyanobacterial-specific factors. Moreover, expression of CikA mutant variants that distribute diffusely results in the striking delocalization of KaiC.
  
  
  CONCLUSIONS
  This work shows that the cyanobacterial circadian system undergoes a circadian orchestration of subcellular organization. We propose that the observed spatiotemporal localization pattern represents a novel layer of regulation that contributes to the robustness of the clock by facilitating protein complex formation and synchronizing the clock with environmental stimuli.
authors.affiliation: Center for Circadian Biology, University of California, San Diego, La Jolla, CA 92093, USA; Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Susan E
authors.initials: SE
authors.lastname: Cohen
authors.affiliation: Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Marcella L
authors.initials: ML
authors.lastname: Erb
authors.affiliation: Department of Bioengineering and San Diego Center for Systems Biology, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Jangir
authors.initials: J
authors.lastname: Selimkhanov
authors.affiliation: Center for Circadian Biology, University of California, San Diego, La Jolla, CA 92093, USA; Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Guogang
authors.initials: G
authors.lastname: Dong
authors.affiliation: Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA; Department of Bioengineering and San Diego Center for Systems Biology, University of California, San Diego, La Jolla, CA 92093, USA; BioCircuits Institute, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Jeff
authors.initials: J
authors.lastname: Hasty
authors.affiliation: Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Joe
authors.initials: J
authors.lastname: Pogliano
authors.affiliation: Center for Circadian Biology, University of California, San Diego, La Jolla, CA 92093, USA; Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA. Electronic address: sgolden@ucsd.edu.
authors.forename: Susan S
authors.initials: SS
authors.lastname: Golden
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002940:Circadian Rhythm; D056925:Circadian Rhythm Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism; D015151:Immunoblotting; D008856:Microscopy, Fluorescence; D016133:Polymerase Chain Reaction; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport; D046940:Synechococcus / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D056925:Circadian Rhythm Signaling Peptides and Proteins; C114269:KaiA protein, cyanobacteria; C114271:KaiC protein, cyanobacteria; D011494:Protein Kinases; C411989:CikA protein, bacteria