Functional significance of FRH in regulating the phosphorylation and stability of Neurospora circadian clock protein FRQ.
FREQUENCY (FRQ) is the central component of the Neurospora circadian clock. All FRQ proteins form the FFC complex with FRH (FRQ-interacting RNA helicase) that acts as the negative element in the circadian negative feedback loop by repressing frq mRNA levels. To understand the function of the FRQ-FRH interaction, we mapped and identified the minimal FRQ region that is required for FRQ-FRH interaction. We demonstrated that the FRQ-FRH complex formation is required for the interaction between FRQ and the White Collar Complex (WCC) and clock function. On the other hand, in the FRQ-FRH complex, FRQ is also required for the FRH-WCC interaction. Disruption of FRQ-FRH interaction or down-regulation of FRH results in hypophosphorylation, rapid degradation of FRQ, as well as low levels of WHITE COLLAR-1 and WHITE COLLAR-2. Furthermore, we showed that the rapid FRQ degradation in the absence of FRH is independent of FWD-1, the ubiquitin E3 ligase of FRQ under normal conditions, thus uncovering an alternative pathway for FRQ degradation.
Guo
Jinhu
J
Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA.
Cheng
Ping
P
Liu
Yi
Y
D000595:Amino Acid Sequence; D002940:Circadian Rhythm; D005656:Fungal Proteins / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D020868:Gene Silencing; D008954:Models, Biological; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009154:Mutation; D009491:Neurospora / Q000378:metabolism*; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D020365:RNA Helicases / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism
C087405:FRQ protein, Neurospora crassa; D005656:Fungal Proteins; D044767:Ubiquitin-Protein Ligases; D020365:RNA Helicases