Wu Colin G, Spies Maria
Department of Biochemistry, University of Iowa Carver College of Medicine, 51 Newton Rd., 4-532 BSB, Iowa City, IA 52242, USA.
Department of Biochemistry, University of Iowa Carver College of Medicine, 51 Newton Rd., 4-532 BSB, Iowa City, IA 52242, USA
Nucleic Acids Res. 2016 Oct 14;44(18):8742-8753. doi: 10.1093/nar/gkw574. Epub 2016 Jun 24.
Guanine rich nucleic acid sequences can form G-quadruplex (G4) structures that interfere with DNA replication, repair and RNA transcription. The human FANCJ helicase contributes to maintaining genomic integrity by promoting DNA replication through G4-forming DNA regions. Here, we combined single-molecule and ensemble biochemical analysis to show that FANCJ possesses a G4-specific recognition site. Through this interaction, FANCJ targets G4-containing DNA where its helicase and G4-binding activities enable repeated rounds of stepwise G4-unfolding and refolding. In contrast to other G4-remodeling enzymes, FANCJ partially stabilizes the G-quadruplex. This would preserve the substrate for the REV1 translesion DNA synthesis polymerase to incorporate cytosine across from a replication-stalling G-quadruplex. The residues responsible for G-quadruplex recognition also participate in interaction with MLH1 mismatch-repair protein, suggesting that the FANCJ activity supporting replication and its participation in DNA interstrand crosslink repair and/or heteroduplex rejection are mutually exclusive. Our findings not only describe the mechanism by which FANCJ recognizes G-quadruplexes and mediates their stepwise unfolding, but also explain how FANCJ chooses between supporting DNA repair versus promoting DNA replication through G-rich sequences.
富含鸟嘌呤的核酸序列可形成G-四链体（G4）结构，干扰DNA复制、修复及RNA转录。人类FANCJ解旋酶通过促进DNA在形成G4的DNA区域进行复制，从而有助于维持基因组完整性。在此，我们结合单分子和整体生化分析表明，FANCJ拥有一个G4特异性识别位点。通过这种相互作用，FANCJ靶向含有G4的DNA，其解旋酶和G4结合活性使得G4能够进行多轮逐步解折叠和重新折叠。与其他G4重塑酶不同，FANCJ可部分稳定G-四链体。这将为REV1跨损伤DNA合成聚合酶保留底物，以便在复制停滞的G-四链体对面掺入胞嘧啶。负责G-四链体识别的残基也参与与MLH1错配修复蛋白的相互作用，这表明支持复制的FANCJ活性及其参与DNA链间交联修复和/或异源双链体排斥是相互排斥的。我们的研究结果不仅描述了FANCJ识别G-四链体并介导其逐步解折叠的机制，还解释了FANCJ如何在支持DNA修复与通过富含G的序列促进DNA复制之间做出选择。
