One loxP site was inserted upstream of exon 2 (containing the SH3 domain) and a floxed neomycin resistance cassette was inserted downstream. Mice were bred to Tg(EIIa-cre)C5379Lmgd expressing mice to excise exon 2 and the selection cassette. Normal transcription is observed on Northern blots but protein levels are less than 10% of levels in control mice. (J:178190)