To generate an allele in which the expression of the beta isoform is completely ablated while the expression of the alpha isoform is maintained, cDNA encoding the C-terminal of the alpha 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 beta isoform. The levels of alpha isoform transcript and protein were equivalent to those detected in wild-type mice.