A STOP codon and coding sequence for haemaglutinin (HA) epitope tag were inserted in frame before the start of the GK domain at amino acid 500. In addition, a floxed neo cassette was inserted downstream to replace sequence and this cassette was subsequently excised by Cre leaving a single loxP site after the STOP codon. Western blot and immunoprecipitation analysis confirmed the absence of protein in hippocampal extracts from homozygous mice. RT-PCR analysis indicated that a very low level of mRNA expression (less than 5% of wild-type) was present in hippocampal extracts from homozygous mice.