CONTROL OF THE EXPRESSION OF THE ADE2 GENE OF THE YEAST SACCHAROMYCES-CEREVISIAE

The ADE2 gene encodes AIR-carboxylase which catalyzes the sixth step o f the purine biosynthetic pathway in Saccharomyces cerevisiae. We have analyzed the effect of deletions in the promoter region of this gene on the expression of the enzyme using a fusion of the ADE2 gene promot er to the bacterial lacZ gene. Adenine added to the growth medium repr essed the expression of the fusion at the level of mRNA. The ADE2-lacZ fusion expression can be slightly activated in response to aminoacid starvation, but only in Gcn4(+) strains and in an adenine-supplemented medium. In the absence of adenine in the medium ADE2 gene expression is derepressed, and neither starvation for histidine nor a gcd1 genera l control regulatory mutation leads to additional derepression. Our ex periments indicate that the ADE2 gene of the purine biosynthetic pathw ay is under both specific adenine control and the general amino-acid c ontrol system. The cis-acting promoter elements mediating both modes o f regulation overlap each other and are located around, the proximal T GACTC sequence.