A neo cassette was inserted into exon 4 at nucleotide 7292 via homologous recombination. Northern blot and quantitative RT-PCR confirmed a 50% reduction in wild-type transcript and detected an aberrant message consisting of a splicing between exon 3 and the downstream neo cassette/exon 4 boundary in heterozygotes. Western blot analysis of kidney homogenates from homozygotes confirmed the absence of protein. (J:138969)