UASt regulatory sequences drive expression of an engineered Ser cDNA. 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.