ACTIVATION AND REPRESSION OF THE YEAST ARO3 GENE BY GLOBAL TRANSCRIPTION FACTORS

The ARO3 gene of Saccharomyces cerevisiae codes for the phenylalanine-inhibited 3-deoxy-D-arabinoheptulosonate-7-phosphate synthase (EC 4.1.2.15) and is regulated by the general control system of amino acid biosynthesis through a single GCN4-binding site in its promoter. A combined deletion and mutation analysis of the ARO3 promoter region in a Delta gcn4-background revealed two additional regulatory systems involved in ARO3 transcription. The ARO3 gene is (i) activated through a sequence element which binds the multifunctional DNA-binding protein ABF1 in vitro and (ii) repressed through an URS1 element, which binds the same protein in vitro as the URS1 element in the CAR1 promoter. Since both the ABF1-binding site and the URS1 element represent cis-acting elements of global transcription regulatory systems in yeast, the ARO3 gene is the first example of a GCN4-regulated gene which is both activated and repressed by global transcription factors. Activation of the ARO3 gene through the ABF1-binding site and repression through the URS1 element seem to be independent of each other and independent of activation by the GCN4 protein.