Abstract
BackgroundEfficient mechanisms for rejoining of DNA double-strand breaks (DSBs) are vital because misrepair of such lesions leads to mutation, aneuploidy and loss of cell viability. DSB repair is mediated by proteins acting in two major pathways, called homologous recombination and nonhomologous end-joining. Repair efficiency is also modulated by other processes such as sister chromatid cohesion, nucleosome remodeling and DNA damage checkpoints. The total number of genes influencing DSB repair efficiency is unknown.ResultsTo identify new yeast genes affecting DSB repair, genes linked to gamma radiation resistance in previous genome-wide surveys were tested for their impact on repair of site-specific DSBs generated by in vivo expression of EcoRI endonuclease. Eight members of the RAD52 group of DNA repair genes (RAD50, RAD51, RAD52, RAD54, RAD55, RAD57, MRE11 and XRS2) and 73 additional genes were found to be required for efficient repair of EcoRI-induced DSBs in screens utilizing both MATa and MATα deletion strain libraries. Most mutants were also sensitive to the clastogenic chemicals MMS and bleomycin. Several of the non-RAD52 group genes have previously been linked to DNA repair and over half of the genes affect nuclear processes. Many proteins encoded by the protective genes have previously been shown to associate physically with each other and with known DNA repair proteins in high-throughput proteomics studies. A majority of the proteins (64%) share sequence similarity with human proteins, suggesting that they serve similar functions.ConclusionsWe have used a genetic screening approach to detect new genes required for efficient repair of DSBs in Saccharomyces cerevisiae. The findings have spotlighted new genes that are critical for maintenance of genome integrity and are therefore of greatest concern for their potential impact when the corresponding gene orthologs and homologs are inactivated or polymorphic in human cells.
Highlights
Efficient mechanisms for rejoining of DNA double-strand breaks (DSBs) are vital because misrepair of such lesions leads to mutation, aneuploidy and loss of cell viability
Exo1 is a 5’-to’3’ exonuclease active in resection of DSB ends in the homologous recombination pathway and it has other roles in replication and mismatch repair [17,39]
Exo1−/− cells were not detected in the original diploid screens, we have previously observed that exo1 haploid library mutants are gamma-sensitive and human exo1−/− cells are sensitive to ionizing radiation [40]
Summary
Efficient mechanisms for rejoining of DNA double-strand breaks (DSBs) are vital because misrepair of such lesions leads to mutation, aneuploidy and loss of cell viability. Repair efficiency is modulated by other processes such as sister chromatid cohesion, nucleosome remodeling and DNA damage checkpoints. Repair of the damage may be performed by one or more different pathways, depending on the specific type of DNA lesion involved. Most DNA damaging agents that induce DSBs generate other lesions as well, with the other lesions typically occurring at much higher frequencies. Despite their rarity, unrepaired and/or misrepaired DSBs are believed to be the major cause of cell death after exposure to such agents [5,6]
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