Forms the heterodimeric complex core-binding factor (CBF) with RUNX family proteins (RUNX1, RUNX2, and RUNX3). RUNX members modulate the transcription of their target genes through recognizing the core consensus binding sequence 5'-TGTGGT-3', or very rarely, 5'-TGCGGT-3', within their regulatory regions via their runt domain, while CBFB is a non-DNA-binding regulatory subunit that allosterically enhances the sequence-specific DNA-binding capacity of RUNX. The heterodimers bind to the core site of a number of enhancers and promoters, including murine leukemia virus, polyomavirus enhancer, T-cell receptor enhancers, LCK, IL3 and GM-CSF promoters (Probable). CBF complexes repress ZBTB7B transcription factor during cytotoxic (CD8+) T cell development. They bind to RUNX-binding sequence within the ZBTB7B locus acting as transcriptional silencer and allowing for cytotoxic T cell differentiation (PubMed:18258917). Heterodimer with RUNX1, RUNX2 and RUNX3 (Probable). Interacts with COPRS. Found in a complex with PRMT5 and RUNX1 (PubMed:22193545). Expressed in all tissues tested. Highest level in thymus, but also abundantly expressed in muscle, lung and brain. Major isoform. Does not dimerize with the alpha subunit. Does not dimerize with the alpha subunit. Belongs to the CBF-beta family.