CKI and CKII mediate the FREQUENCY-dependent phosphorylation of the WHITE COLLAR complex to close the Neurospora circadian negative feedback loop

Disruption of the interaction between FRQ and CK-1a results in hypophosphorylation of FRQ, WC-1, and WC-2.

• The ck-1a(L) mutant exhibits circadian rhythms of approximately 32 hours due to increased stability of FRQ and delayed phosphorylation.
• Low levels of WC-1 and WC-2 in the ck-1a(L) strain suggest that CK-1a is crucial for maintaining circadian positive feedback loops.
• Hypophosphorylated WCC retains the ability to bind to the C-box within the frq promoter, potentially preventing inactivation through FRQ-mediated phosphorylation.
• In the cka(RIP) strain, which disrupts the catalytic subunit of casein kinase II, WC-1 and WC-2 are also hypophosphorylated, leading to persistent high binding of WCC to the C-box.

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