A null allele was created by replacing the ATG start site within exon 2 with a PGK-neo cassette flanked by lox71 and loxP sites. Besides disrupting the gene, the cassette also serves as an acceptor in recombination mediated cassette exchange (RMCE). RT-PCR confirmed absence of mRNA in the brain, lung, liver, and kidney. Northern blots of liver RNA and Western blots of serum confirmed absence of mRNA and protein, respectively.