Schematic diagram of kit cITDs and their expression in Ba/F3 cells. A human c-KIT fragment spanning nt's 1633 to 1845, containing either wild-type or the cITD1 mutation (indexed with an asterisk), substituted the corresponding murine fragment delimited by the restriction sites BsaBI and NdeI. The predicted amino acid sequences from either the wild-type or the 4 identified cITDs are shown. They affect amino acids 593 to 605 from exon 12 and 572 to 592 from exon 11. cITD2 has an additional P573S point mutation in the exon 11 fragment (bold and boxed; the nucleotide change in parentheses underneath is bold and underlined). Duplicated sequences are underlined; exon 12 sequences are highlighted in gray. EC indicates extracellular domain; TM, transmembrane domain; JM, juxtamembrane domain; TK, tyrosine kinase domain; KI, kinase insert; hmWT, human/mouse wild-type; and cITD, complex internal tandem duplication. The amino terminus is labeled NH₂, and the carboxy terminus is labeled COOH.