Fig. 7.

Helix-1 and phosphorylation of flexible linker in MLL1 IBM are both crucial for MLL1-fusion-driven transformation. (A) Diagrams of MLL1 constructs and mutants used in B and C. (B and C) The colony-forming capacity of murine stem cells transformed with an MLL1-ENL fusion was compared with those transformed with MLL1-ENL mutants in helix-1 (B) or in the flexible linker and FxGF motif (C). CFU of lineage-depleted murine hematopoietic stem cells transduced with vectors carrying the WT or mutated MLL1-ENL fusions were determined in three rounds. Errors bars indicate SDs determined from independent replicates (n = 3). Statistical differences were determined using Student’s t test; *P < 0.05; ns, nonsignificant compared with WT. (D) Summary and conceptual model of IBM affinity switching.