Overview of the kit^D814Vflox transgenic construct. The transgene is based on bacterial artificial chromosome clone RPCI 23–274L11 containing the entire kit genomic sequence along with abundant flanking DNA. The activating point mutation (D814V) was introduced into exon 17, and a loxP-flanked transcriptional/translational stop cassette (STOP) was recombined into intron1–2. The wild-type (wt) kit locus and the transgenic kit allele before (flox Stop) and after Cre-mediated deletion of the stop element (del Stop) are shown. T7 and SP6 indicate promoter fragments at the ends of the vector backbone; and N, NotI restriction site. Sizes are in kilobases (kb), not drawn to scale.