The endogenous gene was targeted with a construct in which codon 217 had been modified by site directed mutagensis to encode glycine rather than valine. The targeted residue (corresponding with Val 205 in the human protein) lies within the N finger domain and is involved in zinc finger protein binding. A floxed neo cassette was inserted in the intron following the exon containing the substitution mutation. Comparision with mice carrying Gata4tm1.1Sho indicated that the intronic neo cassette did not affect gene expression.