Histone methyltransferase that catalyzes methyl group transfer from S-adenosyl-L-methionine to the epsilon-amino group of 'Lys-4' of histone H3 (H3K4) via a non-processive mechanism. Part of chromatin remodeling machinery predominantly forms H3K4me1 and H3K4me2 methylation marks at active chromatin sites where transcription and DNA repair take place (PubMed:25561738, PubMed:17707229). Likely plays a redundant role with KMT2C in enriching H3K4me1 marks on primed and active enhancer elements (PubMed:24081332). Plays a central role in beta-globin locus transcription regulation by being recruited by NFE2 (PubMed:17707229). Plays an important role in controlling bulk H3K4me during oocyte growth and preimplantation development (By similarity). Required during the transcriptionally active period of oocyte growth for the establishment and/or maintenance of bulk H3K4 trimethylation (H3K4me3), global transcriptional silencing that preceeds resumption of meiosis, oocyte survival and normal zygotic genome activation (By similarity). L-lysyl(4)-[histone H3] + S-adenosyl-L-methionine = H(+) + N(6)-methyl-L-lysyl(4)-[histone H3] + S-adenosyl-L-homocysteine N(6)-methyl-L-lysyl(4)-[histone H3] + S-adenosyl-L-methionine = H(+) + N(6),N(6)-dimethyl-L-lysyl(4)-[histone H3] + S-adenosyl-L-homocysteine Component of the menin-associated histone methyltransferase complex, at least composed of KMT2B/MLL4, ASH2L, RBBP5, WDR5, DPY30, MEN1; the complex interacts with POLR2A and POLR2B via MEN1 (PubMed:14992727, PubMed:23508102). Interacts with NFE2 (PubMed:17707229). Interacts with KDM6B (PubMed:17825402). Interacts (via WIN motif) with WDR5 (PubMed:22665483, PubMed:22266653, PubMed:18840606). Interacts (via MBM motif) with MEN1 (PubMed:22327296). Forms a core complex with the evolutionary conserved subcomplex WRAD composed of WDR5, RBBP5, ASH2L/ASH2 and DPY30 subunits; WRAD differentially stimulates the methyltransferase activity (PubMed:25561738). Widely expressed. Highest levels in testis. Also found in brain with higher expression in the cerebellum than in any other region, bone marrow, heart, muscle, kidney, placenta, spleen, thymus, prostate, ovary, intestine, colon, peripheral blood lymphocytes and pancreas. Often amplified in pancreatic carcinomas. The CXXC zinc finger mediates binding to DNA containing unmethylated cytidine-phosphate-guanosine (CpG) dinucleotides. The disease is caused by variants affecting the gene represented in this entry. Belongs to the class V-like SAM-binding methyltransferase superfamily. Histone-lysine methyltransferase family. TRX/MLL subfamily. This protein was first named MLL2 by PubMed:10637508 and PubMed:10409430. MLL2 corresponds to another protein located on chromosome 12 (see AC O14686). Thus, KMT2B/MLL4 is often referred to as MLL2 and vice versa in the literature. Probably cloning artifact.