Figure 2.

Four interlocked feedback loops at the core of the Arabidopsis oscillator. In the central loop, CCA1 and LHY act as negative elements to repress the expression of a positive element TOC1. TOC1 is involved in the positive regulation of CCA1 and LHY, partially through antagonizing CHE through protein interaction. Experimental observations and mathematical modeling have incorporated three interlocked loops on the top of the central loop. CCA1 and LHY repress the expression of ELF3, ELF4 and LUX, which in turn have positive effects on the expression of CCA1 and LHY through unknown mechanism. In the morning loop, PRR7 and PRR9 repress the expression of CCA1 and LHY, which in turn activate PRR7 and PRR9. In the evening loop, GI promotes TOC1 expression, which in turn represses GI. Arrows indicate transcriptional activation and horizontal bars indicate transcriptional repression.