Figure 2.

Constitutive tyrosine phosphorylation of KIT^642Glu. In Ba/F3 cells expressing wild-type KIT, strong tyrosine phosphorylation of KIT occurred only after stimulation by rmSCF. In contrast, KIT^del559–560 and KIT^816Val were phosphorylated even without stimulation by rmSCF, indicating the ligand-independent (constitutive) activation of these mutants. The constitutive tyrosine phosphorylation of KIT^816Val was greater than that of KIT^del559–560. Tyrosine residues of KIT^642Glu were also phosphorylated independently of rmSCF, at a level similar to that of wild-type KIT after stimulation by rmSCF and of KIT^del559–560.