Links between C/EBPα and circadian clock gene expression. The clock mechanism involves transcriptional-translational feedback loops. The transcriptional activators Clock and Bmal1 drive the expression of Per2 and Rev-erbα genes. Per and Cry proteins dimerize in the cytoplasm and enter the nucleus to inhibit the Clock/Bmal1 complexes. Phosphorylation by CKIϵ leads to proteolysis of cytoplasmic Per2. Rev-erbα inhibits bmal1 expression. C/EBPα positively regulates Per2 promoter. Solid thick lines indicate direct regulation; solid thin lines, indirect regulation; and dashed lines, undetermined mode of regulation.