A targeting vector was designed to insert a loxP site upstream and a PGK-neomycin selection cassette flanked by loxP and FRT sites 2 kb downstream of exon 1. The PGK-neo was excised by transient expression of FLP or cre recombinase. The loxP-flanked region encompasses part of the promoter region, the transcription start site, and the first exon. (J:102740)