A region containing exons 4 through 11 was deleted by in vitro cre mediated recombination of a single loxP site inserted in intron 3 and a floxed neo cassette downstream of exon 11. The deleted region encoded the entire kinase domain. A shortened transcript, corresponding to a 0.9 kb deletion, was identified in homozygous mutant mice by Northern blot analysis. (J:80115)