Fig. 1.

Schematic view of the humanized Fech exon 3-4 region joined to a neomycin resistance cassette flanked by loxP sites. The exon 3-4 fragment consists of mouse sequences from intron 2 up to the BspHI site in exon 3 and from the BamHI site in exon 4 into intron 4 (Fig. S2). Mouse exon parts are shown as black boxes, human exon parts as dark gray ones. Note that the Neo cassette is in inverse orientation with respect to the Fech fragment. In the final targeting construct, this part of the assembly was joined to 5′ and 3′ homology regions of 6120 and 6006 bp, containing exons 2 and 5, respectively.