LoxP sites were inserted around exon 3 and a FRT-flanked neomycin cassette was inserted downstream of exon 2. Founder mice were crossed with Flpe transgenic mice to remove the neomycin cassette. Gene expression in the absence of cre was unaffected as demonstrated by immunoblot analysis of homozygote kidney extracts. Cre-mediated removal of exon 3 will lead to an early termination codon in exon 4.