The function of ASH1L (ASH1 like histone lysine methyltransferase, ENSG00000116539) is as follows. Histone methyltransferase specifically trimethylating 'Lys- 36' of histone H3 forming H3K36me3 (PubMed:21239497). Also monomethylates 'Lys-9' of histone H3 (H3K9me1) in vitro (By similarity). The physiological significance of the H3K9me1 activity is unclear (By similarity). {ECO:0000250|UniProtKB:Q99MY8, ECO:0000269|PubMed:21239497}.