title: Analysis of the Fine-Tuning of Cyanobacterial Circadian Phase by Monochromatic Light and Long-Day Conditions.
abstract: The cyanobacterial circadian-related protein, Pex, accumulates in the dark period of the diurnal light-dark cycle. After the diurnal cycle, an approximately 3 h advance in the phase of the circadian bioluminescence rhythm is observed in pex-deficient mutants, as compared with the wild type. However, it is unclear what type of photosensing mechanism regulates the accumulation and the phase change. In monochromatic light irradiation experiments, Pex accumulation was strongly repressed under blue light conditions; however, only small reductions in Pex accumulation were observed under red or green light conditions. After the diurnal cycle of 12 h of white fluorescent light and 12 h of blue light, the phase advance was repressed more than that of the cycle of 12 h red (or green) light. The phase advance also occurred after 16 h light/8 h dark cycles (long-day cycles) but did not occur after 8 h light/16 h dark cycles (short-day cycles). While Pex is a unique winged helix transcription factor harboring secondary structures (α0 and α4 helices), the importance of the structures is not understood. In in vivo experiments with site-directed mutations in the α0 helix, the obtained mutants, in which Pex was missing the hydrophobic side chain at the 28th or 32nd amino acid residue, exhibited no phase delay after the light/dark cycle. In in vitro DNA binding assays, the mutant proteins showed no binding to the promoter region of the clock gene kaiA. From these results, we propose a molecular model which describes the phase delay in cyanobacteria.
authors.affiliation: Department of Life and Environmental System Science, Graduate School of Nanobioscience, Yokohama City University, Yokohama, 236-0027 Japan.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Kobayashi
authors.affiliation: Department of Life and Environmental System Science, Graduate School of Nanobioscience, Yokohama City University, Yokohama, 236-0027 Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Obana
authors.affiliation: Department of Life and Environmental System Science, Graduate School of Nanobioscience, Yokohama City University, Yokohama, 236-0027 Japan.
authors.forename: Naoyuki
authors.initials: N
authors.lastname: Kuboi
authors.affiliation: Division of Biological Science, Graduate School of Science, Nagoya University, Nagoya, 464-8602 Japan.
authors.forename: Yohko
authors.initials: Y
authors.lastname: Kitayama
authors.affiliation: Department of Life and Environmental System Science, Graduate School of Nanobioscience, Yokohama City University, Yokohama, 236-0027 Japan.
authors.forename: Shingo
authors.initials: S
authors.lastname: Hayashi
authors.affiliation: Department of Life and Environmental System Science, Graduate School of Nanobioscience, Yokohama City University, Yokohama, 236-0027 Japan.
authors.forename: Masataka
authors.initials: M
authors.lastname: Oka
authors.affiliation: Department of Life and Environmental System Science, Graduate School of Nanobioscience, Yokohama City University, Yokohama, 236-0027 Japan.
authors.forename: Naomichi
authors.initials: N
authors.lastname: Wada
authors.affiliation: Division of Macromolecular Crystallography, Graduate School of Medical Life Science, Yokohama City University, Yokohama, 230-0045 Japan.
authors.forename: Kyouhei
authors.initials: K
authors.lastname: Arita
authors.affiliation: Division of Macromolecular Crystallography, Graduate School of Medical Life Science, Yokohama City University, Yokohama, 230-0045 Japan Present address: Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo. 113-0033 Japan.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Shimizu
authors.affiliation: Division of Macromolecular Crystallography, Graduate School of Medical Life Science, Yokohama City University, Yokohama, 230-0045 Japan.
authors.forename: Mamoru
authors.initials: M
authors.lastname: Sato
authors.affiliation: Department of Life and Environmental System Science, Graduate School of Nanobioscience, Yokohama City University, Yokohama, 236-0027 Japan.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Kanaly
authors.affiliation: Department of Life and Environmental System Science, Graduate School of Nanobioscience, Yokohama City University, Yokohama, 236-0027 Japan kutsuna@yokohama-cu.ac.jp.
authors.forename: Shinsuke
authors.initials: S
authors.lastname: Kutsuna
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002940:Circadian Rhythm / Q000528:radiation effects*; D015964:Gene Expression Regulation, Bacterial / Q000528:radiation effects*; D008027:Light; D008958:Models, Molecular; D009154:Mutation; D017440:Photoperiod; D011401:Promoter Regions, Genetic / Q000235:genetics; D017433:Protein Structure, Secondary; D016415:Sequence Alignment; D046940:Synechococcus / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects
chemical_list: D001426:Bacterial Proteins; C111941:Pex protein, Synechococcus
keywords: Circadian clock; Cyanobacteria; Day-length; Monochromatic light