Transcriptional feedback of Neurospora circadian clock gene by phosphorylation-dependent inactivation of its transcription factor.
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.
Schafmeier
Tobias
T
Biochemistry Center, University of Heidelberg, Germany.
Haase
Andrea
A
Káldi
Krisztina
K
Scholz
Johanna
J
Fuchs
Marc
M
Brunner
Michael
M
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
C087405:FRQ protein, Neurospora crassa; D005656:Fungal Proteins; D014157:Transcription Factors; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; C118341:RGB-1protein, Neurospora crassa