An A to G substitution resulting in replacement of asparagine at position 965 for a serine (N965S) was introduced in exon 19. A FRT-flanked neomycin selection cassette was inserted upstream of exon 19 (604 bp 5' to the point mutation). Flp-mediated recombination removed the neomycin cassette. This corresponds to a Stargardt disease-associated mutation in the Walker A motif of nuclear binding domain 1. Western blot analysis indicates that the amount of protein expressed in heterozygous photoreceptors is half that of wild-type mice.