The levels of repair of endonuclease III-sensitive sites, 6-4 photoproducts and cyclobutane pyrimidine dimers differ in a point mutant forRAD14, theSaccharomyces cerevisiae homologue of the human gene defective inXPA patients

In the accompanying paper we demonstrated that endonuclease III-sensitive sites in theMAT andHML loci ofSaccharomyces cerevisiae are repaired by the Nucleotide Excision Repair (NER) pathway. In the current report we investigated the repair of endonuclease III sites, 6-4 photoproducts and cyclobutane pyrimidine dimers (CPDs) in arad14-2 point mutant and in arad14 deletion mutant. TheRAD14 gene is the yeast homologue of the human gene that complements the defect in cells from xeroderma pigmentosum (XP) patients belonging to complementation group A. In the point mutant we observed normal repair of endonuclease III sites (i.e. as wild type), but no removal of CPDs at theMAT andHML loci. Similar experiments were undertaken using the recently createdrad14 deletion mutant. Here, neither endonuclease III sites nor CPDs were repaired inMATa orHMRa. Thus the point mutant appears to produce a gene product that permits the repair of endonuclease III sites, but prevents the repair of CPDs. Previously it was found that, in the genome overall, repair of 6-4 photoproducts was less impaired than repair of CPDs in the point mutant. The deletion mutant repairs neither CPDs nor 6-4 photoproducts in the genome overall. This finding is consistent with the RAD14 protein being involved in lesion recognition in yeast. A logical interpretation is that therad14-2 point mutant produces a modified protein that enables the cell to repair endonuclease III sites and 6-4 photoproducts much more efficiently than CPDs. This modified protein may aid studies designed to elucidate the role of the RAD14 protein in lesion recognition.