The targeting vector is designed to introduce an aspartate to alanine (D1994A) substitution at codon 1994 in exon 41 of the endogeneous locus. In addition, an FRT-flanked neomycin resistance (neo) cassette was introduced 400 bp downstream of exon 41. Flp-mediated recombination removed the FRT-flanked neo cassette. (J:101977)