Fig. 7 |. Model for regulation of KaiB association by KaiC phosphostate.

a, Cartoon depiction of the KaiB association pathway. Daytime (yellow) and nighttime (blue) states of KaiC both adopt an extended C₆-symmetric ground state. During the day, the extended state is in equilibrium with an open state where the CII hexamer is destabilized relative to the CI domain. At night, excursions from the extended state result in a C₂-symmetric hexamer where two subunits of the CII domain are compressed to prime KaiC for KaiB association. An initial KaiB binding event takes place through this compressed intermediate to pave the way for cooperative saturation of the CI hexamer with KaiB molecules. b, Schematic depiction of the regulatory conduit through which the CI and CII domains communicate to regulate KaiB association according to clock phase.