This transcriptional activator recognizes and binds to the sequence 5'-RTTAYGTAAY-3' found in the promoter of genes such as albumin, CYP2A4 and CYP2A5. It is not essential for circadian rhythm generation, but modulates important clock output genes. May be a direct target for regulation by the circadian pacemaker component clock. May affect circadian period and sleep regulation (By similarity). Binds DNA as a homodimer or a heterodimer. Can form a heterodimer with TEF (By similarity). Expressed in the suprachiasmatic nuclei (SCN) and in most peripheral tissues, with a strong circadian rhythmicity. Accumulates according to a robust circadian rhythm in liver and kidney. In liver nuclei, the amplitude of daily oscillation has been estimated to be >50-fold, and 2-fold in the brain. Mice deficient for all three PAR bZIP proteins (DBP, HLF and TEF) display a dramatically shortened life span and are highly susceptible to generalized spontaneous and audiogenic epilepsies (due for example to the noise of a vacuum cleaner) that are frequently lethal. The down-regulation of pyridoxal kinase (Pdxk) expression in these mice may participate in this seizure phenotype. Belongs to the bZIP family. PAR subfamily.