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 (By similarity). Likely plays a redundant role with KMT2C in enriching H3K4me1 marks on primed and active enhancer elements (By similarity). Plays a central role in beta-globin locus transcription regulation by being recruited by NFE2 (By similarity). Plays an important role in controlling bulk H3K4me during oocyte growth and preimplantation development (PubMed:20808952). 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 (PubMed:20808952). 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 (By similarity). Interacts with NFE2 (By similarity). Interacts with KDM6B (By similarity). Interacts (via WIN motif) with WDR5 (By similarity). Interacts (via MBM motif) with MEN1 (By similarity). The CXXC zinc finger mediates binding to DNA containing unmethylated cytidine-phosphate-guanosine (CpG) dinucleotides. Females are infertile due to anovulation and follicle loss. Oocytes show reduced H3K4me3 but not H3K4me1, abnormal expression of pro-apoptotic genes and Iap elements (which may contribute to oocyte death and, ultimately, follicle loss) and fail to establish transcriptional repression. Belongs to the class V-like SAM-binding methyltransferase superfamily. Histone-lysine methyltransferase family. TRX/MLL subfamily. The human ortholog, KMT2B/MLL4, was first named MLL2 (see AC Q9UMN6). Thus, mouse Kmt2b/Mll4 is also often referred to as Mll2 and vice versa in the literature. Possible contaminating sequence. The N-terminal 3 residues and C-terminal 8 residues do not match the underlying genomic sequence.