Strand-selective repair of DNA damage in the yeast GAL7 gene requires RNA polymerase II.

We examined the role of transcription in directing repair of DNA damage in active genes by comparing the repair of thymine glycols produced by H2O2 and of UV-induced pyrimidine dimers on each strand of the GAL7 gene of Saccharomyces cerevisiae. Repair of both thymine glycols and pyrimidine dimers on the transcribed strand of the gene occurs two to three times faster than on its nontranscribed strand or in the genome overall. When the gene is inactive, no preferential or strand-selective repair is observed. Using a yeast strain containing a temperature-sensitive mutation in one of the subunits of RNA polymerase II, we find that inactivating RNA polymerase II by shifting the cells to the nonpermissive temperature during repair eliminates the strand selectivity of repair under conditions where repair on the nontranscribed strand of the gene and in the genome overall are only slightly affected. Our observation of strand-selective repair of thymine glycols in the GAL7 gene is the first evidence that this repair process occurs for a nonbulky lesion. In addition, we demonstrate that the transcriptional complex plays a critical role in directing repair to the transcribed strand of active genes.