Transcriptional corepressor. May specifically inhibit gene expression when recruited to promoter regions by sequence-specific DNA-binding proteins such as BCL6 and MLLT3. This repression may be mediated at least in part by histone deacetylase activities which can associate with this corepressor. Involved in the repression of TFAP2A; impairs binding of BCL6 and KDM2B to TFAP2A promoter regions. Via repression of TFAP2A acts as a negative regulator of osteo-dentiogenic capacity in adult stem cells; the function implies inhibition of methylation on histone H3 'Lys-4' (H3K4me3) and 'Lys-36' (H3K36me2) (By similarity). Interacts with CPNE4 (via VWFA domain) (PubMed:12522145). Isoform 1 may interact with MLLT3/AF9 (PubMed:12776190). Interacts with BCL6; the interaction is direct. Forms ternary complexes with BCL6 and SMRT/NCOR2 on selected target genes promoters; potently repress expression. Can interact with HDAC1, HDAC3 and HDAC5. Interacts with PCGF1; the interaction is direct. Interacts with KDM2B. Component of an approximately 800 kDa repressive BCOR complex at least composed of BCOR, RYBP, PCGF1, RING1, RNF2/RING2, KDM2B and SKP1 (By similarity). Expressed in heart, liver, lung, skeletal muscle, spleen and testis. Belongs to the BCOR family. Extended N-terminus.