Coiled-coil domain-mediated FRQ-FRQ interaction is essential for its circadian clock function in Neurospora.

The frequency (frq) gene, the central component of the frq-based circadian negative feedback loop, regulates various aspects of the circadian clock in NEUROSPORA: However, the biochemical function of its protein products, FRQ, is poorly understood. In this study, we demonstrated that the most conserved region of FRQ forms a coiled-coil domain. FRQ interacts with itself in vivo, and the deletion of the coiled-coil region results in loss of the interaction. Point mutations, which are designed to disrupt the coiled-coil structure, weaken or completely abolish the FRQ self-association and lead to the arrhythmicity of the overt rhythm. Mutations of the FRQ coiled-coil that inhibit self-association also prevent its interaction with two other key components of the NEUROSPORA: circadian clock, namely WC-1 and WC-2, the two PAS domain-containing transcription factors. Taken together, these data strongly suggest that the formation of the FRQ-FRQ and FRQ-WC complexes is essential for the function of the NEUROSPORA: clock.