DNA-binding protein which modulates activity of several transcription factors including RB1 (retinoblastoma-associated protein) and AR (androgen receptor) (By similarity). May function as part of an mSin3A repressor complex (PubMed:14581478). Has no intrinsic transcriptional activity (By similarity). Plays a role in the regulation of epigenetic modifications at the PWS/AS imprinting center near the SNRPN promoter, where it might function as part of a complex with RB1 and ARID4B (By similarity). Involved in spermatogenesis, together with ARID4B, where it acts as a transcriptional coactivator for AR and enhances expression of genes required for sperm maturation. Regulates expression of the tight junction protein CLDN3 in the testis, which is important for integrity of the blood-testis barrier (By similarity). Plays a role in myeloid homeostasis where it regulates the histone methylation state of bone marrow cells and expression of various genes involved in hematopoiesis. May function as a leukemia suppressor (By similarity). Identified in mSin3A corepressor complexes together with SIN3A, SIN3B, RBBP4, RBBP7, SAP30, BRMS1, HDAC1 and HDAC2 (PubMed:14581478). Interacts with BRMS1 (PubMed:14581478). Interacts with RB1 (PubMed:8414517, PubMed:8455946). Interacts with ARID4B (PubMed:17043311). Interacts with AR (PubMed:23487765). The function of the Tudor-knot domain, also named chromodomain-like, is uncertain (PubMed:22247551, PubMed:29408527). One study suggests that it mediates binding to lysine-methylated histone tails, with strongest affinity for H4K20me3 and H3K36me3 (PubMed:22247551). However, another study failed to find any interaction between this domain and histone H4K20me3 peptide (PubMed:29408527).