The circadian clock is driven by cell-autonomous transcription/translation feedback loops. The BMAL1 transcription factor is an indispensable component of the positive arm of this molecular oscillator in mammals. Here, we present a molecular genetic screening assay for mutant circadian clock proteins that is based on real-time circadian rhythm monitoring in cultured fibroblasts. By using this assay, we identified a domain in the extreme C terminus of BMAL1 that plays an essential role in the rhythmic control of E-box-mediated circadian transcription. Remarkably, the last 43 aa of BMAL1 are required for transcriptional activation, as well as for association with the circadian transcriptional repressor CRYPTOCHROME 1 (CRY1), depending on the coexistence of CLOCK protein. C-terminally truncated BMAL1 mutant proteins still associate with mPER2 (another protein of the negative feedback loop), suggesting that an additional repression mechanism may converge on the N terminus. Taken together, these results suggest that the C-terminal region of BMAL1 is involved in determining the balance between circadian transcriptional activation and suppression.

,
doi.org/10.1073/pnas.0601416103, hdl.handle.net/1765/72640
Proceedings of the National Academy of Sciences of the United States of America
Biophysical Genomics, Department Cell Biology & Genetics

Kiyohara, Y., Tagao, S., Tamanini, F., Morita, A., Sugisawa, Y., Yasuda, M., … Yagita, K. (2006). The BMAL1 C terminus regulates the circadian transcription feedback loop. Proceedings of the National Academy of Sciences of the United States of America, 103(26), 10074–10079. doi:10.1073/pnas.0601416103