Dual functions of FRQ proteins allow them to participate in multiple clock-related feedback loops, shown in green, in the Neurospora clock. The WC-1 and WC-2 proteins form a WCC that activates gene expression in the dark from frq and possibly from clock-controlled genes(ccgs) associated with output and mediates light-induced transcription from frq, ccgs, and wc-1 (gold arrows). frq m
RNA is translated to make FRQ proteins,which have two roles: (i) FRQ feeds back into the nucleus to rapidly block the positive effect of the WCC in driving frq transcription and (ii) FRQ acts to promote the synthesis of new WC-1. Phosphorylation of FRQ triggers its turnover and is a major determinant of period length in the clock. Coupled to these loops in the circadian system (but not shown) is a FRQ-less oscillator or FLO.
Lee K, Loros JL, Dunlap JC. Interconnected feedback loops in the Neurospora circadian system. (2000) Science 289:107-110.