Regulator which is able to repress transcription, possibly via its interaction with a multiprotein chromatin remodeling complex that modifies the chromatin (PubMed:14651845). Its interaction with BRCA2 suggests that it may play a central role in the DNA repair function of BRCA2 (PubMed:14651845). Mediates ligand-dependent transcriptional activation by nuclear hormone receptors (PubMed:19131338). Homodimer (PubMed:15978617). Interacts with the transactivation domain of BRCA2 (PubMed:14651845). Interacts with CBX1 (via chromoshadow domain) (PubMed:14651845, PubMed:16615912). Interacts with ZMYND11 (PubMed:14651845, PubMed:15947784). Does not interact with CBX3 or CBX5 (PubMed:14651845). Component of a nuclear receptor-mediated transcription complex composed of at least ZNF335, CCAR2 and EMSY; the complex stimulates the transcription of nuclear receptor target genes such as SOX9 and HOXA1 (PubMed:19131338). Within the complex interacts with CCAR2 and ZNF335 (PubMed:19131338). Components of this complex may associate with components of a histone methylation complex to form a complex at least composed of ZNF335, HCFC1, CCAR2, EMSY, MKI67, RBBP5, ASH2L and WDR5 (PubMed:19131338). Within this complex, interacts with ASH2L and RBBP5 (PubMed:19131338). Localizes to DNA damage markers in irradiated cells, suggesting that it participates in DNA repair process. O-glycosylated during cytokinesis at sites identical or close to phosphorylation sites, this interferes with the phosphorylation status. Defects in EMSY may be a cause of sporadic breast cancer and higher-grade ovarian cancers. Overexpressed through amplification almost exclusively in sporadic breast cancer (13%) and higher-grade ovarian cancer (17%). Amplification is associated with worse survival, particularly in node-negative breast cancer, suggesting that it may be of prognostic value. Was named EMSY by PubMed:14651845 because the protein sequence contains the word 'SISTER', after the first author's sister, who is a breast cancer nurse.