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. 2022 Feb 3;1(1):93–105. doi: 10.1016/j.gastha.2021.10.008

Figure 2.

Figure 2

The molecular organization of the cellular circadian clock. Proteins encoded by clock genes PER, CLOCK, ARNTL, and CRY interact to create a negative transcription-translation feedback loop. Intracellular levels of CLOCK are maintained during the 24-hour period. High levels of ARNTL at dawn promote the formation of ARNTL-CLOCK heterodimers, which activate the transcription of PER and CRY. Ubiquitylation degrades the accumulated PER in the cytoplasm. CRY accumulates in the cytoplasm during dusk and translocates to the nucleus to inhibit ARNTL-CLOCK–mediated transcription. During the night, the PER-CRY complex is degraded, and the cycle restarts. Library of Science & Medical Illustrations were utilized in part to create this figure. https://creativecommons.org/licenses/by-nc-sa/4.0/.