The MLL-AF9 fusion protein, which interacts with p-TEFb/DOT1l, is not capable of inducing leukemia in recipient mice when introduced into Hoxa9 deficient cells [20], while the cytoplasmic fusion MLL-GAS7 is capable of driving leukemia in cells deficient for either Hoxa9 or Hoxa7 [21]. This evidence concerns the gene MLLT3 and leukemia.