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'. Binds DNA as a homodimer or a heterodimer. Can form a heterodimer with DBP. Expressed exclusively in the rostral portion of the anterior pituitary during embryogenesis. Found in several tissues in juvenile and adult rats. Expressed up to embryonic day 14 and specifically in the anterior pituitary during embryogenesis. Accumulates according to a robust circadian rhythm. Belongs to the bZIP family. PAR subfamily.