Plasmid constructs and Western blot. (A) Schematic representation of constructs. F3, previously designated pMFPK3E¹² is a modified version of pMF3E,9 where the FKBP12 domain has been modified to contain the mutations G89P and I90K. Murine c-kit receptor sequences encode either the full-length 432-amino acid cytoplasmic domain, or the membrane proximal 388 amino acid cytoplasmic domain. (▪), Myristylation peptide; (▧), FKBP12; (▪), intracellular domain of c-kit receptor; (□), HA epitope tag. (B) Western blot of protein extracts from Ba/F3 cell clones expressing the F3 and F3c-kit432 constructs display protein bands of predicted sizes.