The exon encoding isoform 1 (Romk1) was flanked by loxP sites and a PGK neomycin resistance gene and third loxP site was inserted downstream of the floxed exon. Cre-mediated recombination deleted the isoform 1 exon and the neomycin resistance gene while leaving the promoters and exons of isoform 2 (Romk2) and isoform 3 (Romk3) intact. (J:231022)