TISSUE-SPECIFIC EXPRESSION OF THE DIAZEPAM-BINDING INHIBITOR IN DROSOPHILA-MELANOGASTER - CLONING, STRUCTURE, AND LOCALIZATION OF THE GENE

The diazepam-binding inhibitor (DBI; also called acyl coenzyme A-bindi ng protein or endozepine) is a 10-kDa polypeptide found in organisms r anging from yeasts to mammals. It has been shown that DBI and its proc essing products are involved in various specific biological processes such as GABA(A)/benzodiazepine receptor modulation, acyl coenzyme A me tabolism, steroidogenesis, and insulin secretion. We have cloned and s equenced the Drosophila melanogaster gene and cDNA encoding DBI. The D rosophila DBI gene encodes a protein of 86 amino acids that shows 51 t o 56% identity with previously known DBI proteins. The gene is compose d of one noncoding 5' and two coding exons and is localized on the chr omosomal map at position 65E. Several transcription initiation sites w ere detected by RNase protection and primer extension experiments. Com puter analysis of the promoter region revealed features typical of hou sekeeping genes, such as the lack of TATA and CCAAT elements. However, in its low GC content and lack of a CpG island, the region resembles promoters of tissue specific genes. Northern (RNA) analysis revealed t hat the expression of the DBI gene occurred from the larval stage onwa rds throughout the adult stage. In adult flies, DBI mRNA and immunorea ctivity were detected in the cardia, part of the Malpighian tubules, t he fat body, and gametes of both sexes. Developmentally regulated expr ession, disappearing during metamorphosis, was detected in the larval and pupal brains. No expression was detected in the adult nervous syst em. On the basis of the expression of DBI in some but not all tissues, vith high energy consumption, we propose that in D. melanogaster, DBI is involved in energy metabolism in a manner that depends on the subst rate used for energy production.