Department of Pathology and Laboratory Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
Nucleic Acids Res. 2013 Mar 1;41(5):3079-93. doi: 10.1093/nar/gkt016. Epub 2013 Jan 23.
Trans-lesion DNA synthesis (TLS) is a DNA damage-tolerance mechanism that uses low-fidelity DNA polymerases to replicate damaged DNA. The inherited cancer-propensity syndrome xeroderma pigmentosum variant (XPV) results from error-prone TLS of UV-damaged DNA. TLS is initiated when the Rad6/Rad18 complex monoubiquitinates proliferating cell nuclear antigen (PCNA), but the basis for recruitment of Rad18 to PCNA is not completely understood. Here, we show that Rad18 is targeted to PCNA by DNA polymerase eta (Polη), the XPV gene product that is mutated in XPV patients. The C-terminal domain of Polη binds to both Rad18 and PCNA and promotes PCNA monoubiquitination, a function unique to Polη among Y-family TLS polymerases and dissociable from its catalytic activity. Importantly, XPV cells expressing full-length catalytically-inactive Polη exhibit increased recruitment of other error-prone TLS polymerases (Polκ and Polι) after UV irradiation. These results define a novel non-catalytic role for Polη in promoting PCNA monoubiquitination and provide a new potential mechanism for mutagenesis and genome instability in XPV individuals.
跨损伤 DNA 合成 (TLS) 是一种 DNA 损伤容忍机制，它利用低保真度的 DNA 聚合酶来复制受损的 DNA。遗传性癌症倾向综合征着色性干皮病变体 (XPV) 是由于紫外线损伤 DNA 的易错 TLS 所致。当 Rad6/Rad18 复合物单泛素化增殖细胞核抗原 (PCNA) 时，TLS 就会启动，但 Rad18 被招募到 PCNA 的基础尚不完全清楚。在这里，我们发现 XPV 患者突变的 XPV 基因产物 DNA 聚合酶 eta (Polη) 将 Rad18 靶向 PCNA。Polη 的 C 末端结构域与 Rad18 和 PCNA 结合，并促进 PCNA 单泛素化，这是 Y 家族 TLS 聚合酶中 Polη 所特有的功能，与它的催化活性可分离。重要的是，在紫外线照射后，表达全长无催化活性 Polη 的 XPV 细胞会增加其他易错 TLS 聚合酶（Polκ和 Polι）的募集。这些结果定义了 Polη 在促进 PCNA 单泛素化中的一种新的非催化作用，并为 XPV 个体中的突变和基因组不稳定性提供了一个新的潜在机制。
