p53 knockdown in human hematopoietic precursors. (A) Schematic representation of the lentiviral RNA interference vector pTRIPΔU3-EF1α p53. The predicted short hairpin RNA targeting the human p53 is shown. (B) Human hematopoietic progenitors (CD34⁺) were isolated and transduced with the lentiviral vector pTRIPΔU3-EF1α p53 and, after 1 week in culture with cytokines, were sorted based on the expression of GFP. Cells were then γ-irradiated. Six hours later, whole-cell extracts were prepared, separated using 10% SDS-polyacrylamide gel electrophoresis (SDS-PAGE), and immunoblotted to detect human p53. The blot was reprobed with an antibody against β-actin as a loading control.