The exosome regulates circadian gene expression in a posttranscriptional negative feedback loop.

The eukaryotic circadian oscillators consist of autoregulatory negative feedback loops. However, little is known about the role of posttranscriptional regulation of RNA in circadian oscillators. In the Neurospora circadian negative feedback loop, FRQ and FRH form the FFC complex that represses frq transcription. Here, we show that FFC also binds frq RNA and interacts with the exosome to regulate frq RNA decay. Consequently, frq RNA is robustly rhythmic as it is more stable when FRQ levels are low. Silencing of RRP44, the catalytic subunit of the exosome, elevates frq RNA levels and impairs clock function. In addition, rrp44 is a clock-controlled gene and a direct target of the WHITE COLLAR complex, and RRP44 controls the circadian expression of some ccgs. Taken together, these results suggest that FFC and the exosome are part of a posttranscriptional negative feedback loop that regulates frq transcript levels and the circadian output pathway.