YIPPEE/YPEL5 regulates circadian period by modulating PER ubiquitination and stability

Circadian clocks rely on evolutionarily conserved transcriptional-translational feedback loops to align physiology and behavior with the 24-hour day-night cycle. Post-translational modifications, especially ubiquitination, critically control core clock protein stability and circadian pace. In both fruit flies and mammals, the abundance of key pacemaker protein PERIOD (PER/PER2) must be tightly regulated to sustain circadian rhythms. However, the canonical phosphorylation-dependent pathway cannot fully account for turnover of PER in Drosophila. Here we identify Yippee as a critical regulator of PER level through a genetic screen of downregulating ubiquitination pathways. Knockdown of Yippee in circadian pacemaker neurons significantly lengthens the circadian period by [~]2 hours and elevates PER levels. Indeed, YIPPEE physically interacts with PER in fly head. Mechanistically, its mammalian homolog YPEL5 binds PER2, promotes K63-linked polyubiquitination and proteasomal degradation of PER2 independently of FASP-region phosphorylation. Lastly, downregulating YPEL5/Ypel5 prolongs circadian periods in human U2OS cells and mice. Our findings reveal an evolutionarily conserved mechanism in which Yippee/YPEL5 regulates circadian rhythms by mediating ubiquitin-dependent degradation of PER/PER2.