Locke et al (2006) 3 Loop  Arabidopsis Model

 

This model consists of three feedback loops.

In the first loop, LHY transcription has a light-induced component, that is dependent on the concentration of the unknown protein P, and a light-independent component that is activated by the unknown protein X.  Nuclear LHY protein acts as a repressor of  TOC1 transcription. Nuclear TOC1 protein activates protein X transcription and so indirectly activates LHY transcription, completing the loop. Protein P production is switched on during darkness and off during the light period.

In the second loop, nuclear TOC1 protein represses transcription of the unknown protein Y, and nuclear protein Y activates TOC1 transcription. Protein Y transcription is also light-dependent, being greater in the day. This effect is partly mediated by nuclear protein P.

The two loops are interlocked as nuclear LHY protein acts as a repressor of protein Y transcription.

In the third loop, APRR7/9 transcription is activated by LHY protein, and there is also a second light-activated component mediated by protein P. APRR7/9 protein in turn represses LHY transcription.

All RNAs and proteins are degraded enzymatically, according to Michaelis-Menten kinetics. TOC1 protein degradation is inhibited by light. Protein P degradation has two components, a light-dependent linear process, and a light independent Michaelis-Menten process.

All proteins are translated and move reversibly between the nucleus and cytoplasm by linear processes.

This model has been accepted for publication in Molecular Systems Biology