UASt regulatory sequences drive expression of an engineered Ser cDNA. Nucleotides encoding Tyr1248 and Arg1249 are replaced with an XbaI restriction site (which encodes Ser and Arg), and the initiating ATG codon is replaced with a BspH1 restriction site which results in replacing Phe2 with Ile. The endogenous Ser 5'UTR is replaced with a HindIII-NcoI fragment of the Xenopus β-globin gene leader. The 3'UTR of the Ser cDNA is truncated to 17bp 3' of the stop codon and SV40 polyadenylation sequences are present.