STRUCTURE AND REGULATION OF THE CHICKEN ERYTHROID DELTA-AMINOLEVULINATE SYNTHASE GENE

Erythroid cells regulate heme biosynthesis in a manner that is distinc t from all other cell types. While heme negatively regulates the synth esis of the housekeeping delta-aminolevulinate synthase (ALAS-N) in al l non-erythroid cells, the expression of an erythroid-specific isozyme (ALAS-E) is developmentally regulated in red blood cells. As a first step towards understanding the molecular basis for the transcriptional regulation of ALAS-E during erythropoiesis, we cloned and characteriz ed the chicken ALAS-E locus. This gene spans 18 kbp and is composed of eleven exons. The intron/exon structure of erythroid ALAS was found t o be conserved among several vertebrate species. Direct RNA sequencing identified a 5' untranslated region that is derived from two contiguo us exons and is predicted to form a very stable stem-loop structure th at bears resemblance to the ferritin iron-responsive element. Tissue-s pecific expression of the ALAS-E gene was analyzed by transient transf ection assays in hematopoietic cells of both erythroid and non-erythro id origins. These experiments identified distal (- 784 to - 505 bp) an d proximal (- 155 to + 21 bp) promoter elements which are required for high level, erythroid-specific transcription.