Abstract
The HIS7 gene of Saccharomyces cerevisiae encodes a bifunctional glutamine amidotransferase:cyclase catalyzing two reactions that lead to the formation of biosynthetic intermediates of the amino acid histidine and the purine adenine. The HIS7 gene is activated by GCN4p under environmental conditions of amino acid starvation through two synergistic upstream sites GCRE1 and GCRE2. The BAS1p-BAS2p complex activates the HIS7 gene in response to adenine limitation. For this activation the proximal GCN4p-binding site GCRE2 is required. GCN4p and BAS1p bind to GCRE2 in vitro. Under conditions of simultaneous amino acid starvation and adenine limitation the effects of GCN4p and BAS1/2p are additive and both factors are necessary for maximal HIS7 transcription. These results suggest that GCN4p and BAS1/2p are able to act simultaneously through the same DNA sequence in vivo and use this site independently from each other in a non-exclusive manner.
Highlights
Promoters of yeast genes contain two types of transcriptional control elements
An 8-fold reduction was observed when both GCN4p Recognition Elements (GCREs) were mutated (Fig. 3). These results suggest that GCN4p activates HIS7 transcription synergistically through both GCREs under conditions of amino acid starvation
The levels of GCN4p independent HIS7 transcription directed by the promoters mutated in GCRE2 in adenine-deficient growth medium were similar to the levels observed with the strain carrying a wildtype HIS7 promoter allele in adenine containing growth medium (Fig. 4). These results suggest that HIS7 transcription is activated independently of GCN4p through GCRE2 under conditions of adenine limitation
Summary
Promoters of yeast genes contain two types of transcriptional control elements. TATA and initiator elements, located near the transcriptional start site, comprise the binding sites for general transcription factors and the RNA polymerase holoenzyme complex. Co-regulation of genes involved in different metabolic pathways in yeast is usually achieved by the same transcription factor that binds to a common target sequence in the different target promoters. An example of such a cross-pathway regulation is the general control of amino acid biosynthesis in yeast (2). De novo biosynthesis of the amino acid histidine and purines are metabolically interconnected because both pathways share common substrates and intermediates (4) This connection on the metabolic level seems to be reflected by the cross-pathway regulation on transcriptional level of certain HIS and ADE genes by the transcription factors GCN4p and BAS1/BAS2p. Together with BAS1p, BAS2p is involved in the adenine regulation of either purine (5) or amino acid biosynthetic genes
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