Figure 1

Simplified scheme of regulatory interactions of some core Arabidopsis clock components. The morning proteins CCA1/LHY are the sole directly activating elements (red line) in this overview, acting to promote the transcription of PRR9 and PRR7. Repressive relationships (black lines) are based on the papers discussed [3–5] and previously published work. Positioning along the 12-hour:12-hour light:dark time axis approximates the period of maximal protein expression, as does the placement of the PRR/TOC1 names within the respective bars. PRR9 and PRR7 have been grouped separately from PRR5 and TOC1 on the basis of similarities between the partners within each group with respect to single mutant phenotypes, known dimerizations, effects on expression of certain genes and phase of expression. The LUX-ELF3-ELF4 evening complex (EC) consists of a DNA-binding transcription factor (LUX) that requires ELF3 and ELF4 as co-factors for full activity. The co-stabilized GI-ZTL (ZEITLUPE) complex functions to degrade PRR5 and TOC1 proteins, but GI probably has a separate role in its effects on the EC. The dotted line indicates passage of the relational indicator behind the EC bar.