Fig 7. Model: Photocycle length defines the strength of the VVD-WCC interaction and the magnitude of this interacting pool is essential for photoadaptation and maintained light sensitivity.

(1) WCC binds DNA light responsive elements (LRE) after light exposure, and activates the transcription of vvd and wc-1. Light activated chromophores (blue crosses) are shown with orange halo. A portion of WCC is subsequently degraded (6). Newly synthesized WC-1 protein may be light-activated to become part of transcriptionally active WCC (2) or complex with newly synthesized light-activated VVD forming a dynamic pool (3). (4) Ambient light intensity results in some portion of WC-1 undergoing photoreversion to the dark state, allowing future re-activation by light. (5) The length of the VVD photocycle controls the duration of the WCC-VVD interaction and the size of the WCC-VVD pool. This in turn determines how much stabile, light-activated WCC is maintained away from DNA and also available via photoreversion to dark WC-1. Thicknesses of arrows represent relative rates of reactions. Red arrows in the fastest photocycle mutant show rates controlled by increasing rate of adduct decay. See text for more details