Tyrosine phosphorylation of Shc proteins in normal CD34⁺ progenitor cells and leukemic CD34⁺cells. Total cell lysates (20 μg protein) were subjected to Western blot analysis. Phosphotyrosine was identified by antiphosphotyrosine antibody (4G10). Representative blots are shown. The positions of p66^Shc, p52^Shc, and p46^Shc are indicated on the right. Molecular-weight marker bands are indicated on the left. Lanes 1 and 4, enhanced chemiluminescence protein molecular-weight markers; lane 2, Nonstimulated A431 cell lysate; lane 3, epidermal growth factor–stimulated A431 cell lysate; lane 5, CD34⁺ cells from normal BM; lane 6, CD34⁻ cells from normal BM; lane 7, CD34⁺cells from AML patient BM; lane 8, CD34⁻ cells from AML patient BM.