Low levels of c-Myb reduce colony formation of p210^BCR/ABL-transduced marrow progenitors. (A) Methylcellulose colony formation of p210^BCR/ABL-transduced purified Lin⁻ cells (2.5 × 10³/plate) in the presence of optimal cytokine concentrations from c-Myb^f/f or c-Myb^f/d mice. This assay was performed once in duplicate plates. Inset shows c-Myb levels detected by Western blotting. (B) Methylcellulose colony formation of p210^BCR/ABL-transduced Lin⁻Sca-1⁺ cells (5 × 10³cells/plate) isolated from c-Myb^f/f or c-Myb^f/d mice, in the presence of optimal cytokine concentrations. Values (P ≤ .001) are representative of 3 different experiments performed in duplicate.