Acts as a transcriptional repressor. Interacts with MXI1 to repress MYC responsive genes and antagonize MYC oncogenic activities. Interacts with MAD-MAX heterodimers by binding to MAD. The heterodimer then represses transcription by tethering SIN3B to DNA. Also forms a complex with FOXK1 which represses transcription. With FOXK1, regulates cell cycle progression probably by repressing cell cycle inhibitor genes expression. Interacts with FOXK1/MNF, MXI, MAD, NCOR1 and SAP30. Interaction with SUDS3 enhances the interaction with HDAC1 to form a complex. Interacts with CRY1, HCFC1, MAD3, MAD4, MAEL, REST, RNF220 and SETDB1. Interacts with C6orf89 (PubMed:23460338). Interacts with MYT1L (By similarity). Ubiquitinated by RNF220 that leads to proteasomal degradation. Extended N-terminus.