ROLE OF UME6 IN TRANSCRIPTIONAL REGULATION OF A DNA-REPAIR GENE IN SACCHAROMYCES-CEREVISIAE

In Saccharomyces cerevisiae UV radiation and a variety of chemical DNA -damaging agents induce the transcription of specific genes, including several involved in DNA repair. One of the best characterized of thes e genes is PHR1, which encodes the apoenzyme for DNA photolyase. Basal -level and damage-induced expression of PHR1 require an upstream activ ation sequence, UAS(PHR1), which has homology with DRC elements found upstream of at least 19 other DNA repair and DNA metabolism genes in y east, Here we report the identification of the UME6 gene of S. cerevis iae as a regulator of UAS(PHR1) activity. Multiple copies of UME6 stim ulate expression from UAS(PHR1) and the intact PHR1 gene. Surprisingly , the effect of deletion of UME6 is growth phase dependent. In wild-ty pe cells PHR1 is induced in late exponential phase, concomitant with t he initiation of glycogen accumulation that precedes the diauxic shift . Deletion of UME6 abolishes this induction, decreases the steady-stat e concentration of photolyase molecules and PHR1 mRNA, and increases t he UV sensitivity of a rad2 mutant. Despite the fact that UAS(PHR1) do es not contain the URS1 sequence, which has been previously implicated in UME6-mediated transcriptional regulation, we find that Ume6p, bind s to UAS(PHR1) with an affinity and a specificity similar to those see n for a URS1 site. Similar binding is also seen for DRC elements from RAD2, RAD7, and RAD53, suggesting that UME6 contributes to the regulat ed expression of a subset of damage-responsive genes in yeast.