Component of the Set1/Ash2 histone methyltransferase (HMT) complex, a complex that specifically methylates Lys-4 of histone H3, but not if the neighboring Lys-9 residue is already methylated. As part of the MLL1/MLL complex it is involved in methylation and dimethylation at Lys-4 of histone H3. May function as a transcriptional regulator. May play a role in hematopoiesis.
