Foreign transcriptional enhancers in yeast. II. Interplay of the polyomavirus transcriptional enhancer and Saccharomyces cerevisiae promoter elements.

In this paper, to further analyze the function of the polyoma enhancer in Saccharomyces cerevisiae, we use as reporter-genes derivatives of the yeast HIS3 gene flanked by two types of partially deleted promoters: in one, UAS elements are removed by deletion of sequences upstream of nt -80 (pGM3181) in the second both TATA boxes and UAS elements are removed by deletion of sequences upstream of nt -35 (pGM2809). These constructs have been studied both as free plasmids and after integration at the TRP1 chromosomal locus. We find that in general the polyoma holoenhancer (A + B domains) elicits transcription from the physiological HIS3 RNA start sites when the native TATA boxes are present. In contrast, an altered enhancer B-domain from polyoma mutant Py-B78, although active when inserted downstream of the test-gene or when coupled to a pseudopromoter (Ciaramella et al, accompanying manuscript), does not work properly in concert with the native yeast TATA boxes. We describe experiments that suggest an important role for the foreign enhancer in RNA start-site selection in yeast.