A point mutation in exon 32 introduced an amino acid substituation of serine for cysteine at position 1229 (C1229S). This mutation results in an abrogation of catalytic activity. Additionally, an IRES-betageo cassette was inserted into an intron upstream of the point mutation and was subsequently removed by cre-mediated recombination. Expression of the full-length protein was confirmed by western blot analysis on embryonic stem cell extracts. (J:129049)