Transformation properties of c-Myb. (A) Serial replating assay with hematopoietic precursors transduced with empty virus or viruses coding for MLL-ENL, Hoxa9, Meis1, and c-Myb singly or in combination as indicated. Typical results of third-round colonies are shown. (B) MLL-ENL-ERtm cells were transduced with c-Myb or empty control virus. Surface markers c-kit and Gr-1 as well as proliferation rates of the resulting cells were analyzed by FACS (left panel) and cell counts (right panel) before and after inactivation of MLL-ENL by withdrawal of 4-OHT.