Three GCN4 responsive elements act synergistically as upstream and as TATA-like elements in the yeast TRP4 promoter.

The yeast TRP4 promoter contains three responsive elements (GCREs) for the 'general control' transcriptional activator GCN4, which are arranged in two upstream elements, UAS1 (GCRE1) and UAS2 (GCRE2 and GCRE3). A point mutation analysis of these elements revealed that all three GCREs are required for GCN4-dependent transcription, but none are involved in basal transcription. Basal transcription and GCN4-dependent transcription use completely different initiator elements in the TRP4 promoter. UAS1 acts synergistically with UAS2 to activate the GCN4-dependent transcription of TRP4. A consensus TATA box can functionally replace the UAS2 element to allow normal GCN4-dependent transcription, suggesting that UAS2 is analogous to the TATA element of other promoters. GCN4 might therefore activate transcription by exhibiting two alternative functions within the natural TRP4 promoter.