Circadian Clockwork (image) National Institutes of Natural Sciences Share Print E-Mail Caption (A) KaiC forms a hexametric ring structure with 12 ATP molecules (represented by "T"). (B) 3D structure of two KaiC molecules in the ring harboring an ATP analog (PDB ID code: 4O0M). A part of the "tail" (colored by green and orange) is pulled back in the ring core before ATP breakdown. (C) Upon the degradation of ATP (T) into ADP (D), the KaiC tail leaps out from the ring core and captures KaiA. The KaiA binding to the KaiC tail facilitates ADP release and ATP incorporation, leading to the upregulation of autophosphorylation of KaiC as a process of the circadian clockwork. Credit Koichi Kato Usage Restrictions None Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.