Molecular characterization of Drosophila melanogaster dihydropteridine reductase.

Dihydropteridine reductase (DHPR) catalyzes the NAD(P)H-mediated reduction of quinonoid dihydropteridine as a part of pterin-dependent aromatic amino acid hydroxylation. We isolated a fragment of Drosophila DHPR gene by PCR using degenerate primers. By screening a cDNA library, we obtained full-length clones. The predicted amino acid sequence of the Drosophila DHPR protein was highly homologous to other species including human and mouse. In particular, the Tyr-(Xaa)(3)-Lys motif, known as the NAD(P)H binding domain, and most amino acids relevant to quinonoid dihydropteridine binding site are identical to human DHPR. The recombinant DHPR protein expressed in Escherichia coli showed DHPR enzyme activity. Northern blot analysis revealed two transcripts of 1.1 and 0.9 kb. Genomic DNA sequencing revealed that the gene consists of two exons interrupted by a single 96-bp intron. The two transcripts have alternative promoters, both having no putative TATA box or CAAT box, but sharing a common poly(A)(+) signal. The existence of two alternative promoters suggests that each transcript be regulated independently through different stimuli. Further study is needed to examine the expression and function of the two alternative transcripts.