Probably involved in transcriptional regulation. In vitro or as fusion protein with KMT2A/MLL1 has transactivation activity. Binds to cruciform DNA. In cells, binding to unmodified histone H3 regulates DOT1L functions including histone H3 ‘Lys-79’ dimethylation (H3K79me2) and gene activation (PubMed:26439302).