Reduction of drosopterin content caused by a 45-nt insertion in Henna pre-mRNA of Drosophila melanogaster

Phenylalanine hydroxylase is assumed to be a key enzyme in drosopterin metabolism, but direct in vivo evidence to support this hypothesis is still absent. In the present study, we found a new natural recessive purple eye mutant of Drosophila melanogaster, Hn ^bp , which was a 45-nt insertion mutant in the second exon of Henna. The insertion resulted in a predicted protein with 15 additional amino acids as compared to the wild-type protein. Further analysis of protein structure showed that the predicted mutant protein probably had two more β-sheets, which may cause instability of two α-helices near the catalytic centre of the enzyme in the Biopterin-Hydroxyl binding domain. Hn ^bp mutant showed eye color defect with decrease of mRNA level, as well as drosopterin content reduction. The drosopterin defect could be fully rescued by expression of wild type Henna in the Hn ^bp background by GMR-GAL4 UAS-Henna/UAS-Henna:Hn ^bp /Hn ^bp transgenic line. All taken together, it can be concluded that the mutation in Henna is responsible for drosopterin reduction in mutant Hn ^bp , which provides key in vivo evidence to support the hypothesis that Henna is involved in drosopterin synthesis.