title: Light-independent phosphorylation of WHITE COLLAR-1 regulates its function in the Neurospora circadian negative feedback loop.
abstract: Phosphorylation is a major regulatory mechanism controlling circadian clocks. In the Neurospora circadian clock, the PER-ARNT-SIM (PAS) domain-containing transcription factor, WHITE COLLAR (WC)-1, acts both as the blue light photoreceptor of the clock and as a positive element in the circadian negative feedback loop in constant darkness, by activating the transcription of the frequency (frq) gene. To understand the role of WC-1 phosphorylation, five in vivo WC-1 phosphorylation sites, located immediately downstream of the WC-1 zinc finger DNA binding domain, were identified by tandem mass spectrometry using biochemically purified endogenous WC-1 protein. Mutations of these phosphorylation sites suggest that they are major WC-1 phosphorylation sites under constant conditions but are not responsible for the light-induced hyperphosphorylation of WC-1. Although phosphorylation of these sites does not affect the light function of WC-1, strains carrying mutations of these sites show short period, low amplitude, or arrhythmic conidiation rhythms in constant darkness. Furthermore, normal or slightly higher levels of frq mRNA and FRQ proteins were observed in a mutant strain containing mutations of all five sites despite its low WC-1 levels. Together, these data suggest that phosphorylation of these sites negatively regulates the function of WC-1 in the circadian negative feedback loop and is important for the function of the Neurospora circadian clock.
authors.affiliation: Department of Physiology, The University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA.
authors.forename: Qiyang
authors.initials: Q
authors.lastname: He
authors.forename: Hongjun
authors.initials: H
authors.lastname: Shu
authors.forename: Ping
authors.initials: P
authors.lastname: Cheng
authors.forename: She
authors.initials: S
authors.lastname: Chen
authors.forename: Lixin
authors.initials: L
authors.lastname: Wang
authors.forename: Yi
authors.initials: Y
authors.lastname: Liu
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D015153:Blotting, Western; D002940:Circadian Rhythm; D004268:DNA-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D004591:Electrophoresis, Polyacrylamide Gel; D000939:Epitopes / Q000737:chemistry; D025461:Feedback, Physiological; D005656:Fungal Proteins; D015966:Gene Expression Regulation, Fungal; D008027:Light; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D009154:Mutation; D009491:Neurospora / Q000378:metabolism*; D010766:Phosphorylation; D017354:Point Mutation; D012313:RNA / Q000737:chemistry; D012333:RNA, Messenger / Q000378:metabolism; D013997:Time Factors; D014157:Transcription Factors / Q000378:metabolism / Q000502:physiology*; D014158:Transcription, Genetic
chemical_list: D004268:DNA-Binding Proteins; D000939:Epitopes; D005656:Fungal Proteins; D012333:RNA, Messenger; D014157:Transcription Factors; C105589:wc-1 protein, Neurospora crassa; D012313:RNA