title: Identification of Light-Sensitive Phosphorylation Sites on PERIOD That Regulate the Pace of Circadian Rhythms in Drosophila.
abstract: The main components regulating the pace of circadian (≅24 h) clocks in animals are PERIOD (PER) proteins, transcriptional regulators that undergo daily changes in levels and nuclear accumulation by means of complex multisite phosphorylation programs. In the present study, we investigated the function of two phosphorylation sites, at Ser826 and Ser828, located in a putative nuclear localization signal (NLS) on the Drosophila melanogaster PER protein. These sites are phosphorylated by DOUBLETIME (DBT; Drosophila homolog of CK1δ/ε), the key circadian kinase regulating the daily changes in PER stability and phosphorylation. Mutant flies in which phosphorylation at Ser826/Ser828 is blocked manifest behavioral rhythms with periods slightly longer than 1 h and with altered temperature compensation properties. Intriguingly, although phosphorylation at these sites does not influence PER stability, timing of nuclear entry, or transcriptional autoinhibition, the phospho-occupancy at Ser826/Ser828 is rapidly stimulated by light and blocked by TIMELESS (TIM), the major photosensitive clock component in Drosophila and a crucial binding partner of PER. Our findings identify the first phosphorylation sites on core clock proteins that are acutely regulated by photic cues and suggest that some phosphosites on PER proteins can modulate the pace of downstream behavioral rhythms without altering central aspects of the clock mechanism.
authors.affiliation: Graduate Program in Biochemistry, Rutgers University, Center for Advanced Biotechnology and Medicine, Piscataway, New Jersey, USA.
authors.forename: Evrim
authors.initials: E
authors.lastname: Yildirim
authors.affiliation: Rutgers University, Center for Advanced Biotechnology and Medicine, Piscataway, New Jersey, USA.
authors.forename: Joanna C
authors.initials: JC
authors.lastname: Chiu
authors.affiliation: Department of Molecular Biology and Biochemistry, Rutgers University, Center for Advanced Biotechnology and Medicine, Piscataway, New Jersey, USA edery@cabm.rutgers.edu.
authors.forename: Isaac
authors.initials: I
authors.lastname: Edery
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D030801:Animals, Genetically Modified; D002460:Cell Line; D002940:Circadian Rhythm; D029721:Drosophila Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000235:genetics / Q000502:physiology*; D008027:Light; D008969:Molecular Sequence Data; D009154:Mutation; D019913:Nuclear Localization Signals; D056950:Period Circadian Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D012333:RNA, Messenger / Q000235:genetics
chemical_list: D029721:Drosophila Proteins; D019913:Nuclear Localization Signals; C539040:PER protein, Drosophila; D056950:Period Circadian Proteins; D012333:RNA, Messenger