Histone methyltransferase that catalyzes methyl group transfer from S-adenosyl-L-methionine to the epsilon-amino group of 'Lys-4' of histone H3 (H3K4). Part of chromatin remodeling machinery predominantly forms H3K4me1 methylation marks at active chromatin sites where transcription and DNA repair take place. Likely plays a redundant role with KMT2D in enriching H3K4me1 mark on primed and active enhancer elements. L-lysyl(4)-[histone H3] + S-adenosyl-L-methionine = H(+) + N(6)-methyl-L-lysyl(4)-[histone H3] + S-adenosyl-L-homocysteine Component of the MLL3 complex (also named ASCOM complex), at least composed of catalytic subunit KMT2C/MLL3, ASH2L, RBBP5, WDR5, NCOA6, DPY30, KDM6A, PAXIP1/PTIP, PAGR1 and alpha- and beta-tubulin. 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. Interacts (via WIN motif) with WDR5. In adult, detected in testis, kidney, spleen and lung, weakly expressed in brain and absent in heart and liver. First detected throughout the embryo at 8 dpc when expression is strong in forebrain neuroepithelium and absent in heart. Expressed in the eye lens between 10 and 14.5 dpc. By 13 dpc, expressed strongly in spinal cord, hand/foot plates and gonads. The SET domain interacts with histone H3 but not H2A, H2B and H4, and may have a H3 lysine specific methylation activity. Belongs to the class V-like SAM-binding methyltransferase superfamily. Histone-lysine methyltransferase family. TRX/MLL subfamily. Truncated N-terminus.