A point mutation 12 bases downstream of adenine of the start codon was introduced to generate an in-frame stop codon. A mouse phosphoglycerate kinase promoter-driven neomycin resistantance gene (pgkneo) and a prokaryotic em7 promoter-driven zeocin-resistant gene (em7zeo) was inserted downstream of the engineered point mutation. Western blot analysis confirmed the absence of protein expression in the cerebral cortex and sciatic nerve of homozygote mutant mice.