A self excising selection cassette (ACN) was inserted in intron 3 and the bases agg were changed to cgc in exon 4 via homologous recombination. The base changes result in an arginine to glutamine substitution at position 200 (R200Q). Cre mediated recombination in the male germ line removed the selection cassette. Protein expression is similar to wild-type protein but DNA binding is absent.