A loxP site was inserted into exon 1 upstream of the ATG. A cassette containing (5' to 3') a loxP site, an FRT-flanked neo resistance marker, and a myc-tagged Osr2 cDNA with a polyadenylation sequence was inserted downstream of exon 2. Cre-mediated recombination removed part of exon 1 and all of exon 2. (J:173121)