Acts as a transcriptional repressor. May function in the assembly and/or enzymatic activity of the Sin3A corepressor complex or in mediating interactions between the complex and other regulatory complexes (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 ARID4A (PubMed:17043311). Involved in spermatogenesis, together with ARID4A, where it functions as a transcriptional coactivator for AR (androgen receptor) 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 (PubMed:23487765). 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 (PubMed:18728284). Component of a Sin3A corepressor complex consisting of SIN3A, SAP130, SUDS3/SAP45, SAP180, HDAC1 and HDAC2 (By similarity). Interacts with ARID4A (PubMed:17043311). Interacts with AR (PubMed:23487765). Expressed in Sertoli cells of the testis. The C-terminus mediates interaction with mSin3A corepressor complex. The N-terminus is involved in transcriptional repression by HDAC-independent mechanisms. The ARID domain is involved in stabilizing the mSin3A corepressor complex on DNA. Embryonic lethal. Lethality occurs between embryonic day E3.5 and E7.5 (PubMed:17043311). Heterozygous males are fully fertile (PubMed:23487765). Double knockouts of ARID4B heterozygotes with ARID4A homozygotes show various hematological abnormalities, which are more severe than the ARID4A phenotype alone. Hematopoietic stem cell (HSC) and common myeloid progenitor (CMP) counts in bone marrow and spleen are increased. Lymphocyte numbers in spleen are significantly reduced. In peripheral blood, red blood cell counts and lymphocyte counts are reduced. Approximately 83% of animals develop acute myeloid leukemia (AML) and/or myeloid sarcoma. In bone marrow cells, expression of FOXP3 is significantly reduced (PubMed:18728284). Expression of HOXB3, HOXB5, HOXB6, HOXB8 and PITX2 in bone marrow cells is reduced (PubMed:17043311). Males show progressive reduction in fertility from 2 months of age onwards, with reduced testis size and variable defects in seminal vesicle formation. Spermatogenesis is partially blocked from the meiosis II stage onwards leading to reduced numbers of mature spermatozoa. Expression in testis of CLDN3, an androgen receptor-regulated gene, is significantly reduced. Expression of PTGDS is also reduced, whereas expression of INHA and EMB is moderately increased (PubMed:23487765).