THE YEAST RAD2, BUT NOT RAD1, GENE IS INVOLVED IN THE TRANSCRIPTION-COUPLED REPAIR OF THYMINE GLYCOLS

Transcription-coupled repair of H2O2-induced thymine glycols and UV-induced pyrimidine dimers has been shown to occur in the yeast Saccharomyces cerevisiae. In order to determine whether the preferential repair of thymine glycols is carried out by the same nucleotide excision repair complex that removes pyrimidine dimers, we examined the repair of thymine glycols in two yeast mutants, rad1 Delta and rad2 Delta, in which the nucleotide excision repair pathway was disrupted. We find that in both wild-type and a rad1 Delta mutant, repair of thymine glycols occurs faster on the transcribed strand of the GAL7 gene than on the nontranscribed strand. This indicates that transcription-coupled repair can occur in the absence of nucleotide excsion repair and that repair of oxidative DNA damage initiated by an N-glycosylase can be coupled to transcription. In contrast, the initial rate of repair of thymine glycols on the transcribed strand of the GAL7 gene in a rad2 Delta mutant is significantly slower than that for the wild-type cells, with kinetics similar to that of the nontranscribed strand. However, by 60 min post-treatment, the amount of repair on the transcribed strand in the rad2 Delta eventually reaches that of the wild-type cells. We conclude that repair of oxidative DNA damage, such as thymine glycols, can be coupled to transcription and that RAD2 facilitates transcription-coupled repair of oxidative DNA damage in yeast.