The transgene comprises 6.3 kb of genomic DNA containing the entire mouse Lim2 gene, including 399 bp of 5' flanking DNA, with the G-to-T transversion in exon 2 putatively responsible for the dominant total opacity 3 (To3) phenotype. Dot-blot and Southern blot analyses of genomic DNA from transgenic mice indicate presence of two co-integrated copies. RT-PCR of total mouse lens RNA followed by digestion of the PCR product with BstE II, which cuts within the mutant, but not the wildtype, Lim2 cDNA, revealed a low but reproducible ratio of transgenic to wildtype mRNA in lenses from fetal (E18), weanling (P~20) and adult (P>20) transgenic mice.