Figure 1.

Scheme of the Ostreococcus tauri circadian clock model using the Systems Biology Graphical Notation (SBGN, http://www.sbgn.org/).The green and pink boxes represent the TOC1 and CCA1 mRNAs and proteins. Processes are drawn in blue for synthesis, red for degradation, and black for conversion or transport, and may be regulated by one or more components. Hollow arrows, bars and arrows with bars indicate positive and negative regulation and absolute requirement, respectively. TOC1 protein exists in two activation states, with light-regulated conversion from inactive (act@0) to active (act@1). Degradation of TOC1 protein is light-induced and only the active form is degraded. CCA1 protein exists in both the cytosol (nuc@0) and the nucleus (nuc@1), and is subject to light-induced degradation at the same rate in both compartments. ‘acc’ (yellow) is the ‘light accumulator’, which, by regulating TOC1 transcription, links the overall gene expression levels to the amount of light received by the organism.