Transcriptional activation by upstream activator sequences requires distinct interactions with downstream elements in the yeast TRP1 promoter.

The interactions between different upstream activator sequences (UAS) and the downstream transcriptional elements of the TRP1 promoter were studied. We have inserted the UAS from the PGK gene into a series of TRP1 promoter deletions such that the PGK UAS is positioned at various distances upstream from or replaces the TRP1 UAS (UAST1). We show that activation of the TRP1 transcription unit I by the PGK UAS shows a marked position dependence, which is solely a function of the position of the PGKUAS relative to sequences involved in the determination of the RNA initiation sites in the TRP1 promoter. No cooperative activation is seen when both UASs are present in the promoter; the PGK UAS is dominant and is not repressed by the TRP1 negative element. In addition, we show that the PGK and TRP1 UASs interact differently with TATA sequence at the TRP1 RNA initiation site. Our results suggest that these UASs are functionally distinct because they use different mechanisms for activating heterologous promoters.