Restoration of c-Myb expression rescues colony formation of c-Myb^f/d p210^BCR/ABL-transduced marrow progenitors. c-Myb^f/d and c-Myb^f/f Lin⁻Sca-1⁺Kit⁺ cells were transduced with the MigRI/p210^BCR/ABL retrovirus and 24 hours after retroviral transduction sorted for GFP positivity. p210^BCR/ABL-expressing c-Myb^f/d Lin⁻Sca-1⁺Kit⁺ cells were subsequently transduced with a c-Myb/MSCV/puro retrovirus or the empty MSCV/puro vector as a negative control. p210^BCR/ABL-expressing c-Myb^f/f Lin⁻Sca-1⁺Kit⁺ cells were transduced with empty vector MSCV/puro as a positive control. After 24 hours, cells (8 × 10⁴/plate) were plated in methylcellulose in the presence of puromycin (1 μg/mL). Colony formation was assessed 9 days later. Representative of 3 different experiments. P ≤ .001.