Tyrosine phosphorylation and kinase activity of the Kit receptor in serum-starved ELM-I-1 cells. (A) Kit protein was immunoprecipitated from serum-starved cells and from ELM-D cells subsequently stimulated with 10 ng/mL SCF for 10 minutes before cell lysis. Immunoprecipitated proteins were then analyzed by Western blotting using antiphosphotyrosine and anti-Kit receptor antibodies. A control antibody was used in the immunoprecipitation loaded into the right-hand lane. Size markers are shown in kilodaltons. (B) Kit protein was immunoprecipitated from unstimulated ELM-D and ELM-I-1 cells and its autophosphorylation activity was assayed in vitro as described in Materials and Methods.