A single loxP site remained in place of exon 3 after the cre-mediated excision of a floxed region containing exon 3 and an inserted neo cassette. The deleted exon encoded the majority of the protein including the pore- and membrane-spanning domains and the entire N-terminal region and a substantial portion of the C-terminal region. Protein was undetected by Western blot analysis of homozygous mutant brain tissue. (J:77047)