UASt regulatory sequences drive expression of an engineered Dl c1 cDNA. Nucleotides encoding Met619 and Lys620 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 His2 with Asn. The endogenous Dl 5'UTR is replaced with a HindIII-NcoI fragment of the Xenopus β-globin gene leader. The 3'UTR of the Dl c1 cDNA terminates 242bp 3' to the predicted stop codon and SV40 polyadenylation sequences are present.