A T to A mutation was introduced at nucleotide 778 in exon 19 and a floxed neo cassette was inserted in the untranslated region after exon 22 via homologous recombination. Cre mediated recombination removed the neo cassette. Immunoblot analysis indicates reduced protein levels in tissues of homozygous mice. Kinase activity is absent from the mutant protein. (J:256578)