In this study, we investigated not only the relationship between MLL1 and AF9, the most frequent fusion partner of MLL1 in AML, and the role of AF9 in transcriptional regulation in the non-MLLr HEL cells, but also the chromatin occupancy patterns of MLL1 and MLL-AF9, and the role of MLL-AF9 in transcriptional regulation in MLL cells. Here, MLLT3 is linked to acute myeloid leukemia.