CBFA1 (Core-binding factor subunit alpha 1) is a member of the runt/Cbfa family of transcription factors. CBFA1 binds to an osteoblast-specific cis-acting element that activates the expression of the osteoblast-specific gene Osteocalcin. It regulates the expression of all major genes expressed by osteoblasts, and it is a regulator of osteoblast differentiation. Cbfa1 insufficiency is the cause of cleidocranial dysplasia, characterized by bone defects. It is also involved in bone matrix deposition, osteoblast function and maturation, as well as both intramembranous and endochondral ossification. CBF binds to the core site, 5'-PYGPYGGT-3', of a number of enhancers and promoters, including murine leukemia virus, polyomavirus enhancer, T-cell receptor enhancers, osteocalcin, osteopontin, bone sialoprotein, alpha 1(I) collagen, LCK, IL-3 and GM-CSF promoters.