A loxP site was inserted upstream of the pore-S6 domain containing exon. At the same time, a floxed neomycin cassette was introduced downstream. Cells in which transient Cre recombinase expression of properly targeted ES cells resulted in excision of both the neomycin gene and the pore-S6 exon were selected. Both mRNA and protein were shown to be absent in the brains of mice homozygous for this allele. (J:86763)