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 PEBP2alpha subunits, PEBP2alphaA, PEBP2alphaB and PEBP2alphaC, 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 PEBP2beta is the target of chromosomal inversion 16 (p13;q22) with the smooth muscle myosin heavy chain, producing a chimeric gene, PEBP2beta/CBFbeta-SMMHC, that is associated with human acute myeloid leukemia.