Cryptochrome 1 regulates the circadian clock through dynamic interactions with the BMAL1 C terminus

• Published in: Nature structural & molecular biology Vol. 22; no. 6; pp. 476 - 484
• Main Authors: Xu, Haiyan, Gustafson, Chelsea L, Sammons, Patrick J, Khan, Sanjoy K, Parsley, Nicole C, Ramanathan, Chidambaram, Lee, Hsiau-Wei, Liu, Andrew C, Partch, Carrie L
• Format: Journal Article
• Language: English
• Published: New York Nature Publishing Group US 01.06.2015; Nature Publishing Group
• Subjects: 101/6; 38/77; 631/45/535/878/1263; 631/45/612/822; 631/57/2269; 631/80/105; 82/111; 82/29; 96/106; 96/109; Animals; ARNTL Transcription Factors - metabolism; Biochemistry; Biological Microscopy; Cells, Cultured; Circadian Clocks; Circadian rhythm; Circadian rhythms; Cryptochromes - metabolism; Fibroblasts - physiology; Genetic aspects; Humans; Life Sciences; Mammals; Membrane Biology; Mice; Mice, Knockout; Molecular biology; Mutation; Physiological aspects; Protein Structure; Structure; Transcription factors; United States
• ISSN: 1545-9993; 1545-9985
• DOI: 10.1038/nsmb.3018

The mammalian circadian cycle is determined by sequential activation of clock target-gene expression by CLOCK–BMAL and subsequent repression by CRY. Biochemical and NMR data now show that Cry1 competes with coactivators for binding to the BMAL1 transcriptional-activation domain to regulate circadian cycling. The molecular circadian clock in mammals is generated from transcriptional activation by the bHLH-PAS transcription factor CLOCK–BMAL1 and subsequent repression by PERIOD and CRYPTOCHROME (CRY). The mechanism by which CRYs repress CLOCK–BMAL1 to close the negative feedback loop and generate 24-h timing is not known. Here we show that, in mouse fibroblasts, CRY1 competes for binding with coactivators to the intrinsically unstructured C-terminal transactivation domain (TAD) of BMAL1 to establish a functional switch between activation and repression of CLOCK–BMAL1. TAD mutations that alter affinities for co-regulators affect the balance of repression and activation to consequently change the intrinsic circadian period or eliminate cycling altogether. Our results suggest that CRY1 fulfills its role as an essential circadian repressor by sequestering the TAD from coactivators, and they highlight regulation of the BMAL1 TAD as a critical mechanism for establishing circadian timing.