An A to G nucleotide change at position 2564 resulting in an asparagine to serine substitution at amino acid 855 was introduced in exon 24. In addition, a floxed mini-cDNA cassette containing exons 23-56 and human growth hormone poly-A signal was inserted upstream of exon 23. In the absence of cre-recombination, the wild-type protein is expressed. (J:282550)