The genetics of nucleotide excision repair in the yeast Saccharomyces cerevisiae is complex, apparently requiring at least 10 genes. We have isolated 5 of these genes (designated RAD1, RAD2, RAD3, RAD4, and RAD10) by molecular cloning and plan to overexpress them in order to generate proteins for biochemical study. We have sequenced four of these five genes and have noted regions of homology with other proteins in the predicted amino acid sequence of some of them. In particular, there is striking homology between Rad3 protein and a number of prokaryotic and eukaryotic proteins that bind nucleotides and hydrolyze ATP or GTP. Mutations in this region of the RAD3 gene render cells defective in the nucleotide excision repair function. In addition to its role in nucleotide excision repair, the RAD3 gene is essential for the viability of haploid cells in the absence of DNA damage. The nature of the essential function is unknown. The RAD1 and RAD3 genes are not inducible by DNA damaging agents. However, exposure of cells to UV radiation, 4-nitroquinoline 1-oxide, or gamma radiation results in 4- to 6-fold enhanced expression of the RAD2 gene.
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