A loxP site was inserted upstream of the start codon in exon 1. A tandem affinity purification (TAP) tag was inserted downstream of the start codon. An FRT-flanked neomycin resistance cassette with a 3' loxP site was inserted downsteam of exon 1. Flp-mediated recombination removed the selection cassette and left exon 1 floxed. (J:231214)