Bringing It All Together: Coupling Excision Repair to the DNA Damage Checkpoint

Nucleotide excision repair and the ATR‐mediated DNA damage checkpoint are two critical cellular responses to the genotoxic stress induced by ultraviolet (UV) light and are important for cancer prevention. In vivo genetic data indicate that these global responses are coupled. Aziz Sancar et al. developed an in vitro coupled repair‐checkpoint system to analyze the basic steps of these DNA damage stress responses in a biochemically defined system. The minimum set of factors essential for repair‐checkpoint coupling include damaged DNA, the excision repair factors (XPA, XPC, XPF‐ERCC1, XPG, TFIIH, RPA), the 5′‐3′ exonuclease EXO1, and the damage checkpoint proteins ATR‐ATRIP and TopBP1. This coupled repair‐checkpoint system was used to demonstrate that the ~30 nucleotide single‐stranded DNA (ssDNA) gap generated by nucleotide excision repair is enlarged by EXO1 and bound by RPA to generate the signal that activates ATR. Nucleotide excision repair and the ATR‐mediated DNA damage checkpoint are two critical cellular responses to UV‐induced genotoxic stress and are important for cancer prevention. This review summarizes the in vitro coupled repair‐checkpoint system developed by Aziz Sancar et al. to analyze the basic steps of these two DNA damage stress responses in a biochemically defined reaction. They demonstrated that the ~30 nucleotide single‐stranded DNA gap generated during the excision repair process by XPA, XPC, XPF‐ERCC1, XPG, TFIIH, and RPA is enlarged by the exonuclease EXO1 and bound by RPA to generate the signal that activates ATR‐ATRIP in the presence of TOPBP1.