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An unequal crossover event resulted in the insertion of a neomycin selection cassette into intron 18 with no loss of coding sequences. RT-PCR analysis confirmed that correctly spliced transcripts are produced from this allele. Northern blot analysis on mRNA derived from skin samples of homozygous mice demonstrated that transcript expression was reduced approximately five-fold. Immunoprecipitation experiments on fibroblasts isolated from homozygous mice confirmed that a protein was expressed from this allele at reduced levels compared to wild-type. This is a hypomorphic allele. (J:54081)