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 (By similarity). Binds to unmethylated major satellite DNA and is involved in the recruitment of the Polycomb repressive complex 2 (PRC2) to major satellites (PubMed:25457167). Stimulates the ERCC6L translocase and ATPase activities (By similarity). Homooligomer, probably a homooctamer. Interacts with HDAC2 and HDAC3, but not HDAC1. Interacts with SALL4. Interacts with SMARCA5/SNF2H, BAZ2A/TIP5 and USP21 (By similarity). Interacts with the nucleosome remodeling and histone deacetylase (NuRD) repressor complex (PubMed:25457167). Interacts (via BEN domains 1 and 3) with ERCC6L (via N-terminal TPR repeat); the interaction is direct (By similarity). 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. 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-509 by SUMO1, SUMO2 and SUMO3. Sumoylation probably occurs sequentially, with that of Lys-20 preceding that of Lys-509. It does not alter association with heterochromatin, but is required for the repression of transcription.