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

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 rad7Δ and rad23Δ mutations interact epistatically with the excision repair defective rad1Δ mutation, and synergistically with the rad6Δ and rad52Δ mutations that affect the postreplication repair and recombinational repair pathways, respectively. However, the rad7Δrad6Δ and the rad23Δrad6Δ mutants exhibit the same level of UV sensitivity as the radlΔrad6Δ mutant. This observation is of interest since, in contrast to the rad7Δ or the rad23Δ mutations, the rad1Δ 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.