Structure and regulated expression of the delta-aminolevulinate synthase gene from Drosophila melanogaster

The structure of the single copy gene encoding the putative housekeeping is oform of Drosophila melanogaster delta-aminolevulinate synthase (ALAS) has been determined. Southern and immunoblot analyses suggest that only the hou sekeeping isoform of the enzyme exists in Drosophila. We have localized a c ritical region for promoter activity to a sequence of 121 base pairs that c ontains a motif that is potentially recognized by factors of the nuclear re spiratory factor-1 (NRF-1)/P3A2 family, flanked by two AP4 sites. Heme inhi bits the expression of the gene by blocking the interaction of putative reg ulatory proteins to its 5' proximal region, a mechanism different from thos e proposed for other hemin-regulated promoters. Northern and in situ RNA hy bridization experiments show that maternal alas mRNA is stored in the egg; its steady-state level decreases rapidly during the first hours of developm ent and increases again after gastrulation in a period where the synthesis of several mRNAs encoding metabolic enzymes is activated. In the syncytial blastoderm, the alas mRNA is ubiquitously distributed and decreases in abun dance substantially through cellular blastoderm. Late in embryonic developm ent alas shows a specific pattern of expression, with an elevated mRNA leve l in oenocytes, suggesting an important role of these cells in the biosynth esis of hemoproteins in Drosophila.