The complete EGFP coding sequence was inserted in-frame in the first coding exon followed immediately by a cassette containing three stop codons. This same stop codon cassette was also inserted in exon 5 near its 5' end. An FRT site flanked neomycin resistance gene cassette was inserted 246 bp 5' of exon 1 as well. Chimeric mice were subsequently mated to an flp-deleter strain to excise the neo selection cassette. The full length endogenous protein is not expressed.