Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, VA 22908, USA.
Mol Cell. 2010 Jan 15;37(1):143-9. doi: 10.1016/j.molcel.2009.12.018.
Monoubiquitination of proliferating cell nuclear antigen (PCNA) is a critical posttranslational modification essential for DNA repair by translesion DNA synthesis (TLS). The Rad18 E3 ubiquitin ligase cooperates with the E2 Rad6 to monoubiquitinate PCNA in response to DNA damage. How PCNA is monoubiquitinated in unperturbed cells and whether this plays a role in the repair of DNA associated with replication is not known. We show that the CRL4(Cdt2) E3 ubiquitin ligase complex promotes PCNA monoubiqutination in proliferating cells in the absence of external DNA damage independent of Rad18. PCNA monoubiquitination via CRL4(Cdt2) is constitutively antagonized by the action of the ubiquitin-specific protease 1 (USP1). In vitro, CRL4(Cdt2) monoubiquitinates PCNA at Lys164, the same residue that is monoubiquitinated by Rad18. Significantly, CRL4(Cdt2) is required for TLS in nondamaged cells via a mechanism that is dependent on PCNA monoubiquitination. We propose that CRL4(Cdt2) regulates PCNA-dependent TLS associated with stresses accompanying DNA replication.
多泛素化的增殖细胞核抗原（PCNA）是跨损伤 DNA 合成（TLS）修复所必需的关键翻译后修饰。Rad18 E3 泛素连接酶与 E2 Rad6 合作，在 DNA 损伤后对 PCNA 进行单泛素化。在未受干扰的细胞中，PCNA 如何被单泛素化，以及这是否在与复制相关的 DNA 修复中发挥作用尚不清楚。我们表明，在没有外部 DNA 损伤的情况下，CRL4（Cdt2）E3 泛素连接酶复合物在增殖细胞中促进 PCNA 单泛素化，而不依赖 Rad18。CRL4（Cdt2）通过 USP1 的作用，持续拮抗 PCNA 的单泛素化。在体外，CRL4（Cdt2）在赖氨酸 164 处单泛素化 PCNA，这与 Rad18 单泛素化的残基相同。重要的是，CRL4（Cdt2）通过依赖于 PCNA 单泛素化的机制，在未受损的细胞中对 TLS 是必需的。我们提出，CRL4（Cdt2）调节与 DNA 复制伴随的应激相关的 PCNA 依赖性 TLS。
