An FRT flanked neomycin resistance cassette was inserted upstream of exon3 and exons 3 to 5 were flanked by loxP sites. The floxed exons were subsequently excised by crossing to Tg(EIIa-cre)C5379Lmgd mice. Absence of transcript was confirmed by RT-PCR and Northern blot analysis. Absence of full length protein was shown by Western blot analysis. (J:167848)