The PCNA binding domain of Rad2p plays a role in mutagenesis by modulating the cell cycle in response to DNA damage

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The xeroderma pigmentosum group G (XPG) gene, encoding an essential element in nucleotide excision repair (NER), has a proliferating cell nuclear antigen-binding domain (PCNA-BD) at its C-terminal region. However, the role of this domain is controversial because its presence does not affect NER. Using yeast RAD2, a homolog of human XPG, we show that Rad2p interacts with PCNA through its PCNA-BD and the PCNA-BD of Rad2p plays a role in UV-induced mutagenesis. While a mutation of Rad2p endonuclease activity alone causes dramatically increased mutation rates and UV sensitivity, as well as growth retardation after UV irradiation, a mutation of the Rad2p PCNA-BD in the same mutant causes dramatically decreased mutation rates, reduced UV sensitivity and increased growth rate after UV irradiation. After UV irradiation, large-budded cells of Rad2p endonuclease defective mutants wane due to a mutation of the Rad2p PCNA-BD. Besides, the Rad2p PCNA-BD mutant protein exhibits alleviated PCNA-binding efficiency. These results show a hitherto unsuspected role of the Rad2p PCNA-BD that controls mutagenesis via cell cycle modulation together with PCNA. Furthermore, the high mutation rate of cells with other NER gene mutations was also decreased by the mutation of the Rad2p PCNA-BD, which indicates that the Rad2p-PCNA interaction might be responsible for mutagenesis control in the general NER pathway. Our results suggest that the drastically increased incidence of skin cancer in xeroderma pigmentosum patients could arise from the synergistic effects between cell cycle arrest due to the XPG-PCNA interaction and the accumulation of damaged DNA via defects in DNA damage repair.