The part of exon 2 encoding amino acids 1 through 346 was replaced with an FRT flanked DTR-EGFP cassette and a cre recombinase gene witha nuclear localization sequence. Subsequent flp mediated recombination removed the DTR-EGFP cassette and brought the cre recombinase under the control of the endogenous gene promoter. (J:167075, J:186624, J:207456)