Exons 3 through 5 were replaced by a neomycin selection cassette. The deleted region encompassed 429 bp encoding the second transmembrane domain and a portion of the pore region. While normal transcript was undetected by semi-quantitative RT-PCR analysis, low levels of an aberrant transcript in which exon 2 spliced to exon 6 were observed in homozygous mutant embryos. (J:62797)