Cooperation between the SH3 and the BH domain of p85α is not required for BMMC maturation. (A) Schematic of full-length p85α and p85α mutants lacking either the SH3 or the BH domain. Full-length p85α or p85α mutants lacking either the amino terminal SH3 domain (1-80 aa) or the BH domain (102-288 aa) were cloned into a bicistronic retroviral vector MIEG3. The constructs were HA tagged at the amino terminus to distinguish exogenous expression from endogenous p85 protein. (B) Expression of full-length p85α or p85α mutants. MCps from p85α^−/− mice were transduced with vector, full-length p85α, or p85α mutants lacking either the SH3 domain (p85αΔSH3) or the BH domain (p85αΔBH) and sorted to homogeneity. Cells were harvested and subjected to Western blot analysis using an anti-HA antibody or β-actin antibody as indicated. Expression of various p85α mutants is indicated in the top panel. (C-D) Expression of p85α mutants into p85α^−/− MCps corrects defective mast cell differentiation. Cells in panel B were sorted to homogeneity and grown. At indicated times, maturation was evaluated by staining the cells with antibodies that recognize KIT and IgE receptor by flow cytometry. Shown is a representative dot blot (C) and quantitative data (D) from 5 independent experiments. *P < .05, WT versus p85α^−/−vector.