The sequence encoding the final three C-terminal residues (arginine-glycine-threonine) that are necessary for interaction with Src kinase were replaced with sequence encoding cysteine-glycine-lysine (EGK) isolated from the Itgb1 locus. This mutation was predicted to be interact with other Src family protein tyrosine kinases. Targeting constructs also contained several silent mutations to introduce new HpaI and NdeI restriction sites and a floxed neomycin-resistance cassette between exons 14 and 15. Mice carrying the correctly targeted allele were crossed with cre transgenic mice to remove the neomycin selection cassette. Extracellular protein expression levels on homozygous platelets was 125% of wild-type levels.