Molecular cloning and characterization of hemolymph 3-dehydroecdysone 3beta-reductase from the cotton leafworm, Spodoptera littoralis. A new member of the third superfamily of oxidoreductases.

The primary product of the prothoracic glands of last instar larvae of Spodoptera littoralis is 3-dehydroecdysone (3DE). After secretion, 3DE is reduced to ecdysone by 3DE 3beta-reductase in the hemolymph. We have previously purified and characterized 3DE 3beta-reductase from the hemolymph of S. littoralis. In this study, cDNA clones encoding the enzyme were obtained by reverse transcription-polymerase chain reaction, employing primers based on the amino acid sequences, in conjunction with 5'- and 3'-rapid amplification of cDNA ends. Multiple polyadenylation signals and AT-rich elements were found in the 3'-untranslated region, suggesting that this region may have a role in regulation of expression of the gene. Conceptual translation and amino acid sequence analysis suggest that 3DE 3beta-reductase from S. littoralis is a new member of the third superfamily of oxidoreductases. Northern analysis shows that 3DE 3beta-reductase mRNA transcripts are widely distributed, but are differentially expressed, in some tissues. The developmental profile of the mRNA revealed that the gene encoding 3DE 3beta-reductase is only transcribed in the second half of the last larval instar and that this fluctuation in expression accounts for the change in the enzyme activity during the instar. Southern analysis indicates that the 3DE 3beta-reductase is encoded by a single gene, which probably contains at least one intron.