A single loxp site was inserted upstream of the exon encoding the pore-forming alpha subunit, and a floxed neo-TK cassette downstream. Transient cre-expression excised the floxed region including the exon and neo-TK. Southern blot and PCR confirmed recombination and Western blot of brain membrane proteins from mutants indicated absence of the C-terminus of the alpha subunit. (J:91427)