Two mutually exclusive regulatory systems inhibit UASGATA, a cluster of 5′-GAT(A/T)A-3′ upstream from theUGA4gene ofSaccharomyces cerevisiae

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Abstract
The S. cerevisiae Uga43(Dal80) protein down-regulates the expression of multiple nitrogen pathway genes. It contains a zinc-finger motif similar to the DNA-binding domain of the vertebrate GATA family of transcription factors; this domain is known to direct binding to 5'-GATA-3' core sequences. The inducible UGA4 gene, which encodes the specific gamma-aminobutyrate permease, undergoes strong repression by Uga43p. This study shows that the 5' region of UGA4 contains a UAS element made of four directly repeated 5'-CGAT(A/T) AG-3' sequences. This element, called UASGATA, can potentially confer to the UGA4 gene high-level expression in the absence of inducer, but this potential activity is inhibited by two distinct repression systems. One system is Uga43p-dependent; it operates in cells grown on a poor nitrogen source. The other is the nitrogen repression system, which relies on Ure2p and glutamine and operates when a good nitrogen source is present. Nitrogen repression also blocks the synthesis of Uga43p, making the two repression systems mutually exclusive. Previous studies have shown that expression supported by 5'-GATA-3'-containing UAS elements requires Gln3p, another global nitrogen regulatory factor containing a GATA zinc-finger domain. Although Gln3p contributes to UASGATA activity, evidence suggests that a second factor can potentially direct expression through UASGATA. Expression conferred by this putative factor is subject to both Uga43p- and Ure2p-mediated repression. The role of UASGATA in the expression of the UGA4 gene is discussed in relation to its sensitivity to the two distinct repression systems.