A genomic fragment containing part of exon 2 was replaced with a neomycin selection cassette. RT-PCR analysis indicated that an abnormal transcript is made from this allele that splices exon 1 to exon 3. This abnormal splicing pattern is predicted to result in a frameshift mutation. Western blot analysis on brain extracts derived from homozygous mice demostrated that no stable full length protein is produced from this allele.