PIT1 is a pituitary-specific transcription factor responsible for pituitary development and hormone expression in mammals and is a member of the POU family of transcription factors that regulate mammalian development. The POU family is so named because the first 3 members identified were PIT1 and OCT1 of mammals, and Unc-86 of C. elegans .

PIT1 contains 2 protein domains, termed POU-specific and POU-homeo, which are both necessary for high-affinity DNA binding on genes encoding growth hormone (GH;) and prolactin (PRL). PIT1 is also important for regulation of the genes encoding prolactin and thyroid-stimulating hormone beta subunit (TSHB) by thyrotropin-releasing hormone (TRH) and cyclic AMP.