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Mol Cell. 2017 Sep 7;67(5):770-782.e6. doi: 10.1016/j.molcel.2017.07.017.

Macromolecular Assemblies of the Mammalian Circadian Clock.

Author information

1
Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA.
2
Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA.
3
Laboratory of Molecular Electron Microscopy, Rockefeller University, New York, NY 10065, USA.
4
Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA. Electronic address: cweitz@hms.harvard.edu.

Abstract

The mammalian circadian clock is built on a feedback loop in which PER and CRY proteins repress their own transcription. We found that in mouse liver nuclei all three PERs, both CRYs, and Casein Kinase-1δ (CK1δ) are present together in an ∼1.9-MDa repressor assembly that quantitatively incorporates its CLOCK-BMAL1 transcription factor target. Prior to incorporation, CLOCK-BMAL1 exists in an ∼750-kDa complex. Single-particle electron microscopy (EM) revealed nuclear PER complexes purified from mouse liver to be quasi-spherical ∼40-nm structures. In the cytoplasm, PERs, CRYs, and CK1δ were distributed into several complexes of ∼0.9-1.1 MDa that appear to constitute an assembly pathway regulated by GAPVD1, a cytoplasmic trafficking factor. Single-particle EM of two purified cytoplasmic PER complexes revealed ∼20-nm and ∼25-nm structures, respectively, characterized by flexibly tethered globular domains. Our results define the macromolecular assemblies comprising the circadian feedback loop and provide an initial structural view of endogenous eukaryotic clock machinery.

PMID:
28886335
PMCID:
PMC5679067
DOI:
10.1016/j.molcel.2017.07.017
[Indexed for MEDLINE]
Free PMC Article

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