The transcription factor Polyomavirus enhancer binding protein 2 (PEBP2), also designated Osf2 (Osteoblast-specific transcription factor), CBFA1 (Core Binding Factor) and AML3 (Acute myeloid leukemia), is composed of two subunits, (alpha) and (beta), which are essential for the regulation of hematopoiesis and osteogenesis. The PEBP2(alpha) subunits, PEBP2(alpha)A, PEBP2(alpha)B and PEBP2(alpha)C, are encoded by three RUNX genes, all of which contain a 128-amino acid region homologous to the highly conserved Drosophila segmentation gene, runt. This region is involved in DNA binding and heterodimerization with the regulatory (beta) subunit, which facilitates DNA binding of the (alpha) subunit. Both subunits are required for in vivo function; the disruption of either gene results in a lack of definitive hematopoiesis followed by embryo death in utero due to hemorrhage in the central nervous system. The gene encoding PEBP2(beta) is the target of chromosomal inversion 16 (p13;q22) with the smooth muscle myosin heavy chain, producing a chimeric gene, PEBP2(beta)/CBF(beta)-SMMHC, that is associated with human acute myeloid leukemia.