This model consists of two 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 is probably PIF3. Its 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.
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.