Transcription factor that binds to and transactivates the TSHB promoter. Binds to a minimal DNA-binding sequence 5'-[TC][AG][AG]TTA[TC][AG]-3' (By similarity). Also activates the telokin promoter in smooth muscle-specific and calcium-dependent manner. Binds DNA as a homodimer or a heterodimer. Can form a heterodimer with DBP (By similarity). Isoform Alpha and isoform Beta are expressed at high levels in lung, bladder, kidney, gut and brain. Accumulates according to a robust circadian rhythm in liver and kidney. In liver nuclei, the amplitude of daily oscillation has been estimated to be 9-fold. Expressed at nearly constant level 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.