SETD1A is a SET domain-containing methyltransferase involved in the epigenetic regulation of transcription(PMID:12670868). It is the main catalytic component of a multiprotein complex that methylates lysine 4 of histone H3, a histone mark associated with gene activation (PMID:29937342). Responsible for H3K4me3 enriched promoters and transcriptional programming of inner mass stem cells and neuron progenitors during embryogenesis (PMID:31197650). Does not methylate 'Lys-4' of histone H3 if the neighboring 'Lys-9' residue is already methylated (PubMed:12670868). SETD1A has a calculated molecular weight of 186 kDa, and a 258 kDa band was also reported (PMID: 31076518).