PIT1 is part of the POU family of transcription factors.  It is expressed by somatotrophic cells, as well as thyrotrophs and lactotrophs of the anterior pituitary gland.  It contains a C-terminal domain for transactivation.  Another domain is DNA binding—its C-terminal portion is homologous to the homeodomain consensus, common to many genes involved in development, while the other portion is POU specific, affords PIT1 specificity in its transcriptional activation of the prolactin and growth hormone genes and is involved in protein-protein interactions.  Activity on thyroid stimulating hormone-beta expression is also known for PIT1.