To generate an allele in which the expression of the alpha isoform is completely ablated while the expression of the beta isoform is maintained, cDNA encoding the C-terminal of the beta isoform, as well as a polyA-neo cassette, was inserted into exon 20. RT-PCR and Western blot analyses of homozygous mutant liver confirmed the absence of the alpha isoform. Comparisions with the level of alpha isoform transcript and protein in wild-type mice indicated that while the level of beta isoform transcript is equivalent, the level of beta isoform protein is reduced.