A 4.5 kb region of the gene including exon 1, which encode amino acids 1-518 including the whole motor region and half of the alpha-helical coiled coil domains, was replaced with a PGK-neo cassette via homologous recombination. Western blot analyis of brain lysates using antibodies directed against the C-terminus of the protein confirmed the absence of gene expression in homozygous mutant animals. (J:70607)