Both 1° AML-3 and 1° MPAL-1 carry a KMT2A–AF9 fusion protein, whereas KOPN-8 carries a KMT2A–ENL fusion, suggesting that the AF9 fusion partner recruits particularly high levels of DOT1L to oncoprotein target loci while other leukemias can be variable for DOT1L recruitment. Here, MLLT1 is linked to leukemia.