Fig. 1.

Gene targeting of adm. (A) Structure of the wild-type allele as found in mouse chromosome 7. The 4 exons of the adm gene are represented as solid boxes. Southern probes at the 5′ and 3′ ends of the construct are also indicated. (B) Targeting vector designed to insert loxP sequences (arrowheads) around the adm gene and the neomycin cassette (neo) surrounded by frt sequences (vertical rectangles). An additional BamHI site was added next to the first loxP to allow for identification. The TK gene was also added as a negative marker. A thinner line represents vector sequences. (C) Structure of the modified allele in the ES cells after recombination takes place. (D) Structure of the final allele, following the crossing with Flp expressing mice. P1 (AMD sense) and P2 (AMD antisense) are the primers for diagnostic PCR described in Table S1.