CDNA CLONING AND CHROMOSOME MAPPING OF HUMAN DIHYDROPYRIMIDINE DEHYDROGENASE, AN ENZYME ASSOCIATED WITH 5-FLUOROURACIL TOXICITY AND CONGENITAL THYMINE URACILURIA

The pig and human dihydropyrimidine dehydrogenase (DPD) cDNAs were clo ned and sequenced. The pig enzyme, expressed in Escherichia coli, cata lyzed the reduction of uracil, thymine, and 5-fluorouracil with kineti cs approximating those published for the enzyme purified from mammalia n liver. DPD could be expressed in significant quantities only when ur acil was added to the bacterial growth medium. The pig and human enzym es contained 1025 amino acids and calculated M(r) = 111,416 and 111,39 8, respectively. Conserved domains corresponding to a possible NADPH b inding site and FAD binding site were found in the NH2-terminal half o f the proteins and two motifs of putative [4Fe-4S] binding sites were found near to the carboxyl terminus of the enzyme. The latter correspo nds to the labile COOH-terminal fragment previously shown to contain t he iron sulfur centers. A sequence encompassing a peptide correspondin g to the uracil binding site was found between the NADPH/FAD-containin g NH2-terminal portion of the protein and the iron-sulfur binding site s near to the COOH terminus. Thus, the DPD appears to be derived from at least three distinct domains. The DPYD gene was localized to the ce ntromeric region of human chromosome 1 between 1p22 and q21.