Free α-globin is ubiquitinated in β-thalassemic erythroid cells. Immunoprecipitation-Western blot analysis of solubilized α-globin aggregates from Th3/+ erythrocytes. Membrane-associated α-globin was isolated from mouse Th3/+ (A,C) or human β-thalassemia major (B,D) erythrocytes and solubilized in SDS. Samples were immunoprecipitated with anti–α-globin (A-B) or anti-ubiquitin (C-D) Abs and analyzed by Western blotting using the indicated Abs. Input fractions and preimmune serum (IgG) immunoprecipitation are included as controls. Immunoprecipitation reactions containing purified α-globin or β-globin competitors demonstrate Ab specificity.