An in-frame lacZ gene with a nuclear localization signal was inserted into exon 1c of the gene. A loxP flanked neomycin resistance and Angiotensin-cre cassette (ACN) was inserted following the lacZ gene. The neomycin/cre cassette was autocatalytically removed in the male germline by activation of the Ace promoter in testis. RNase protection assays on liver RNA from homozygous mice demonstrated that the 1c isoform transcript was not detectable, while expression of the 1a isoform was unaffected. Western blot analysis confirmed that the expression of the encoded protein was greatly reduced from this allele; in addition, beta-galactosidase expression was detected from this allele in frozen liver sections.