The speed of circadian clocks in animals is tightly linked to complex phosphorylation programs that drive daily cycles in the levels of PERIOD (PER) proteins. Using Drosophila, we identify a time-delay circuit based on hierarchical phosphorylation that controls the daily downswing in PER abundance. Phosphorylation by the NEMO/NLK kinase at the "per-short" domain on PER stimulates phosphorylation by DOUBLETIME (DBT/CK1δ/ε) at several nearby sites. This multisite phosphorylation operates in a spatially oriented and graded manner to delay progressive phosphorylation by DBT at other more distal sites on PER, including those required for recognition by the F box protein SLIMB/β-TrCP and proteasomal degradation. Highly phosphorylated PER has a more open structure, suggesting that progressive increases in global phosphorylation contribute to the timing mechanism by slowly increasing PER susceptibility to degradation. Our findings identify NEMO as a clock kinase and demonstrate that long-range interactions between functionally distinct phospho-clusters collaborate to set clock speed.
Bibliographical noteFunding Information:
We thank Paul Hardin (Texas A&M, USA) for communicating unpublished results ( Yu et al., 2011 ), Thomas Kusch (Rutgers University, USA) for Sfx cells, and the VDRC (Vienna, Austria) for RNAi lines. We thank Axel Diernfellner and Michael Brunner (Heidelberg University, Germany) for conditions for limited proteolysis. This work was supported by NIH grant (R01NS03498) to I.E. and NIH grant (K99/R00NS061952) to J.C.C.
All Science Journal Classification (ASJC) codes
- Biochemistry, Genetics and Molecular Biology(all)