Interactions of the RAD7 and RAD23 excision repair genes of Saccharomyces cerevisiae with DNA repair genes in different epistasis groups

Summary The RAD7 and RAD23 genes of S. cerevisiae affect the efficiency of excision repair of UV-damaged DNA. We have examined the UV survival of strains carrying the rad7 or rad23 deletion mutation in combination with deletion mutations in genes affecting different DNA repair pathways. As expected, the rad7 and rad23 mutations interact epistatically with the excision repair defective rad1 mutation, and synergistically with the rad6 and rad52 mutations that affect the postreplication repair and recombinational repair pathways, respectively. However, the rad7rad6 and the rad23rad6 mutants exhibit the same level of UV sensitivity as the radlrad6 mutant. This observation is of interest since, in contrast to the rad7 or the rad23 mutations, the rad1 mutant is very UV sensitive and highly excision defective. This observation suggests that RAD6 and RAD7 and RAD23 genes compete for the same substrate during DNA repair.