ABSTRACT
Various post-translational modifications have been identified that play a role in the function of circadian clocks. Among these, phosphorylation has been investigated extensively. It was shown that phosphorylation influences half-life, subcellular localisation, transcriptional activity and conformation of clock components over the course of a circadian day. Recent observations also indicate that time-of-day specific sequential phosphorylation of the Neurospora crassa clock protein FREQUENCY is crucial for measuring time and thus for establishing a robust circadian rhythm. The circadian clock of Neurospora is one of the best-investigated molecular clocks to date. In this review, we summarise the data on what is known so far about the role of phosphorylation of proteins involved in the Neurospora circadian clock.
Subject(s)
Circadian Clocks , Neurospora crassa/metabolism , Animals , Feedback, Physiological , Fungal Proteins/chemistry , Fungal Proteins/metabolism , Intracellular Space/metabolism , Neurospora crassa/cytology , Neurospora crassa/enzymology , Neurospora crassa/physiology , PhosphorylationABSTRACT
Frequency (FRQ) and its transcriptional activator, the White Collar Complex (WCC), are essential components of interconnected feedback loops of the circadian clock of Neurospora. In a negative feedback loop, FRQ inhibits the WCC by recruiting casein kinase 1a (CK1a) and supporting its phosphorylation. In an interconnected positive loop, FRQ supports accumulation of high levels of WCC. Phosphorylation of clock proteins is crucial for the temporal and spatial coordination of these functions. We identified three isoforms of CK1a generated by alternative splicing that all interact with FRQ. Furthermore, we show that WC-2 is phosphorylated by CK1a in vitro and that WC-2 phosphorylation is inhibited in vivo by the CK1-specific inhibitor IC261. Finally, we demonstrate that CK1a activity regulates levels of WC-2.
