A neomycin resistance cassette replaced 1.7 kb of genomic sequence including the 3' half of exon 5, and exons 6 and 7, removing the portion of the gene that encodes amino acids 212-343. Western blot analysis using a carboxy terminal specific antibody did not detect protein in brain tissue from homozygous mutant mice. RT-PCR analysis of brain did not detect expression in homozygous mutant mice.