Transcriptional repressor which associates with the NoRC (nucleolar remodeling complex) complex and plays a key role in repressing rDNA transcription. The sumoylated form modulates the stability of the NoRC complex component BAZ2A/TIP5 by controlling its USP21-mediated deubiquitination (PubMed:21914818, PubMed:26100909). Binds to unmethylated major satellite DNA and is involved in the recruitment of the Polycomb repressive complex 2 (PRC2) to major satellites (By similarity). Stimulates the ERCC6L translocase and ATPase activities (PubMed:28977671). Homooligomer, probably a homooctamer (PubMed:28977671). Interacts with HDAC2 and HDAC3, but not HDAC1. Interacts with SALL4 (PubMed:21914818). Interacts with SMARCA5/SNF2H, BAZ2A/TIP5 and USP21 (PubMed:26100909). Interacts with the nucleosome remodeling and histone deacetylase (NuRD) repressor complex (By similarity). Interacts (via BEN domains 1 and 3) with ERCC6L (via N-terminal TPR repeat); the interaction is direct (PubMed:28977671). In the nucleus, observed in heterochromatic foci containing CBX1, CBX3, CBX5 and histone H3 trimethylated at 'Lys-9'. Released from chromatin during decondensation. Association with heterochromatin does not depend on sumoylation. Expressed at least in heart, kidney, liver, ovary and spleen, with highest levels in spleen and lowest in heart. Expressed on the surface of T-cells. The BEN domain 4 is necessary and sufficient for the localization of BEND3 to heterochromatic regions. Sumoylated at Lys-20 by SUMO1 and at Lys-512 by SUMO1, SUMO2 and SUMO3. Sumoylation probably occurs sequentially, with that of Lys-20 preceding that of Lys-512. It does not alter association with heterochromatin, but is required for the repression of transcription.