To examine the importance of DOT1L recruitment by MLL-AF9 in leukemia cell proliferation, Dot1lf/f CreER-T2+ MLL-AF9 cell lines expressing wild-type DOT1L and DOT1L mutants (Δ10 deletion, I867A, and RCR) were grown in IL-3-conditioned media in the presence of 4-OHT to inactivate endogenous Dot1l. This evidence concerns the gene MLLT3 and leukemia.