Figure 1. MLL1 fusion proteins induce leukemia together with the wild-type MLL1. The wild-type MLL1 complex pre-binds to the promoters of oncogenes H0XA9 and MEIS1 and is required for proper transcription activation of these genes. The MLL1 fusion proteins are associated with Menin, AFF4, and other proteins in the cell. The MLL1 fusion complex constantly activates the expression of H0XA9 and MEIS1, leading to induction of leukemia.