A floxed neo cassette was inserted within intron 4, and genomic sequence with deleted alternatively spliced exon 3 was introduced by homologous recombination. Replaced mutation caused the entire exon 3, necessary for BimEL isoform transcription, to be deleted. The neo cassette was then excised with cre recombinase, leaving a single loxP site in intron 4. By immunoblot analyses, no BimEL proteins were expressed; however, increased amounts of BimL proteins was expressed. This is BimEL isoform specific knock-out allele. (J:137061)