A single point mutation deleting valine 558 was introduced to exon 11 and a floxed neo cassette was introduced to intron 9 via homologous recombination. This point mutation mimics a valine 559 deletion found in a case of human somatic gastrointestinal stromal tumor (GIST). The floxed neo cassette was subsequently removed by mating mutant animals to cre deleter strain TgN(EIIa-cre)C5379Lmgd. The integrity of the V558 deletion was confirmed by DNA sequence analysis.