Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan, Republic of China; Department of Biological Science and Technology, National Chiao Tung University, Hsinchu, Taiwan, Republic of China.
Department of Clinical Laboratory Sciences and Medical Biotechnology, College of Medicine, National Taiwan University, Taipei, Taiwan, Republic of China.
PLoS Biol. 2014 Mar 4;12(3):e1001803. doi: 10.1371/journal.pbio.1001803. eCollection 2014 Mar.
DNA repair mechanisms are essential for preservation of genome integrity. However, it is not clear how DNA are selected and processed at broken ends by exonucleases during repair pathways. Here we show that the DnaQ-like exonuclease RNase T is critical for Escherichia coli resistance to various DNA-damaging agents and UV radiation. RNase T specifically trims the 3' end of structured DNA, including bulge, bubble, and Y-structured DNA, and it can work with Endonuclease V to restore the deaminated base in an inosine-containing heteroduplex DNA. Crystal structure analyses further reveal how RNase T recognizes the bulge DNA by inserting a phenylalanine into the bulge, and as a result the 3' end of blunt-end bulge DNA can be digested by RNase T. In contrast, the homodimeric RNase T interacts with the Y-structured DNA by a different binding mode via a single protomer so that the 3' overhang of the Y-structured DNA can be trimmed closely to the duplex region. Our data suggest that RNase T likely processes bulge and bubble DNA in the Endonuclease V-dependent DNA repair, whereas it processes Y-structured DNA in UV-induced and various other DNA repair pathways. This study thus provides mechanistic insights for RNase T and thousands of DnaQ-like exonucleases in DNA 3'-end processing.
DNA 修复机制对于基因组完整性的维持至关重要。然而，目前尚不清楚在修复途径中，外切核酸酶如何选择和处理断裂末端的 DNA。在这里，我们发现 DnaQ 样外切核酸酶 RNase T 对于大肠杆菌抵抗各种 DNA 损伤剂和紫外线辐射至关重要。RNase T 特异性地修剪包括凸起、泡和 Y 型结构的 DNA 的 3'端，并且它可以与内切核酸酶 V 一起恢复含脱氨酶的肌苷的异源双链 DNA 中的碱基。晶体结构分析进一步揭示了 RNase T 如何通过将苯丙氨酸插入凸起来识别凸起 DNA，结果可以消化末端平齐的凸起 DNA 的 3'端。相比之下，同二聚体的 RNase T 通过单个单体以不同的结合模式与 Y 型结构 DNA 相互作用，从而可以将 Y 型结构 DNA 的 3'突出端紧密修剪到双链区域。我们的数据表明，RNase T 可能在 Endonuclease V 依赖性 DNA 修复中处理凸起和泡状 DNA，而在紫外线诱导的和各种其他 DNA 修复途径中处理 Y 型结构 DNA。因此，本研究为 RNase T 以及数千种 DnaQ 样外切核酸酶在 DNA 3'-端加工中的作用提供了机制见解。
Zotero 插件
