Nucleotides 1745 to 2033, encompassing portions of exons 10 and 11 and the intervening intron, were replaced with a neomycin selection cassette. RT-PCR and sequence analyses identified an aberrant transcript containing the first 569 codons of the endogenous gene fused to 75 neo codons. This transcript was undetected by Northern blot analysis, indicating that it was unstable.