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 (PubMed:17355966, PubMed:25561738). Part of chromatin remodeling machinery, forms H3K4me1, H3K4me2 and H3K4me3 methylation marks at active chromatin sites where transcription and DNA repair take place (PubMed:17355966, PubMed:25561738). Plays an essential role in regulating the transcriptional programming of multipotent hematopoietic progenitor cells and lymphoid lineage specification during hematopoiesis (By similarity). {ECO:0000250|UniProtKB:Q8CFT2, ECO:0000269|PubMed:17355966, ECO:0000269|PubMed:25561738}. This is the function of SETD1B (SET domain containing 1B, histone lysine methyltransferase, Ensembl gene identifier ENSG00000139718).