The Neurospora Circadian System

Neurospora crassa features a complex circadian clock system involving the protein interactions of FRQ and White Collar proteins.

• The core circadian clock feedback loop involves a heterodimer of White Collar-1 (WC-1) and WC-2 proteins that function as both a photoreceptor and a transcription factor.
• The frq gene is expressed in darkness by the WC-1/WC-2 dimer, while the FRQ protein creates a negative feedback loop by inhibiting its own activators.
• Phosphorylation of FRQ by various kinases results in its degradation, which allows the WC-1/WC-2 dimer to reactivate frq expression and restart the circadian cycle.
• Light exposure rapidly induces frq expression, while elevated temperatures can reset the clock by increasing FRQ levels.
• Several FRQ-less oscillators have been identified that regulate Neurospora growth and development independently of the circadian system.

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