title: Transcriptional feedback of Neurospora circadian clock gene by phosphorylation-dependent inactivation of its transcription factor.
abstract: The circadian clock protein Frequency (FRQ) feedback-regulates its own expression by inhibiting its transcriptional activator, White Collar Complex (WCC). We present evidence that FRQ regulates the bulk of WCC through modulation of its phosphorylation status rather than via direct complex formation. In the absence of FRQ, WCC is hypophosphorylated and transcriptionally active, while WCC is hyperphosphorylated and transcriptionally inactive when FRQ is expressed. The phosphorylation status of WCC changes rhythmically over a circadian cycle. Dephosphorylation and activation of WCC depend on protein phosphatase 2A (PP2A), and WCC is a substrate of PP2A in vitro. Hypophosphorylated WCC binds to the clock box of the frq promoter even in the presence of FRQ, while binding of hyperphosphorylated WCC is compromised even when FRQ is depleted. We propose that negative feedback in the circadian clock of Neurospora is mediated by FRQ, which rhythmically promotes phosphorylation of WCC, functionally equivalent to a cyclin recruiting cyclin-dependent kinase to its targets.
authors.affiliation: Biochemistry Center, University of Heidelberg, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Schafmeier
authors.forename: Andrea
authors.initials: A
authors.lastname: Haase
authors.forename: Krisztina
authors.initials: K
authors.lastname: Káldi
authors.forename: Johanna
authors.initials: J
authors.lastname: Scholz
authors.forename: Marc
authors.initials: M
authors.lastname: Fuchs
authors.forename: Michael
authors.initials: M
authors.lastname: Brunner
mesh_terms: D002940:Circadian Rhythm / Q000235:genetics*; D015180:Electrophoresis, Gel, Two-Dimensional; D024202:Electrophoretic Mobility Shift Assay; D025461:Feedback, Physiological; D005656:Fungal Proteins / Q000378:metabolism*; D009492:Neurospora crassa / Q000378:metabolism* / Q000648:ultrastructure; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D054648:Protein Phosphatase 2; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: C087405:FRQ protein, Neurospora crassa; D005656:Fungal Proteins; D014157:Transcription Factors; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; C118341:RGB-1protein, Neurospora crassa