Figure 3. Revised model of the LHY–TOC1 feedback loop [72,73].
Mathematical analysis indicates that the additional components X and Y are required in order to form a robust oscillator that matches the properties of the Arabidopsis clock. X is a gene that is required for the activation of LHY by TOC1. Y is a hypothetical gene that is activated by light and in turn activates TOC1. Y is repressed by both TOC1 and LHY. GI is a candidate for the identity of Y. X is currently unknown. Arrows represent positive regulatory steps, perpendicular lines indicate negative interactions. Genes are represented by rectangles and proteins as ovals.