Molecular and Cellular Biology Laboratory, The Salk Institute for Biological Studies, 10010 North Torrey Pines Road, La Jolla, CA 92037, USA.
Mol Cell. 2011 Apr 22;42(2):224-36. doi: 10.1016/j.molcel.2011.03.015.
Recent evidence for 5'-cytosine (C)-rich overhangs at the telomeres of the nematode Caenorhabditis elegans provided the impetus to re-examine the end structure of mammalian telomeres. Two-dimensional (2D) gel electrophoresis, single telomere-length analysis (STELA), and strand-specific exonuclease assays revealed the presence of a 5'-C-rich overhang at the telomeres of human and mouse chromosomes. C-overhangs were prominent in G1/S arrested as well as terminally differentiated cells, indicating that they did not represent replication intermediates. C-rich overhangs were far more prevalent in tumor cells engaged in the alternative lengthening of telomeres (ALT) pathway of telomere maintenance, which relies on the homologous recombination (HR) machinery. Transient siRNA-based depletion of the HR-specific proteins RAD51, RAD52, and XRCC3 resulted in changes in C-overhang levels, implicating the involvement of 5'-C-overhangs in the HR-dependent pathway of telomere maintenance.
最近有证据表明线虫秀丽隐杆线虫的端粒 5'-胞嘧啶（C）丰富的突出端，这促使人们重新检查哺乳动物端粒的末端结构。二维（2D）凝胶电泳、单端粒长度分析（STELA）和链特异性核酸外切酶分析显示，人类和小鼠染色体的端粒存在 5'-C 丰富的突出端。在 G1/S 期阻滞以及终末分化细胞中，C 突出端非常明显，这表明它们不是复制中间体。在参与端粒维持的替代性延长（ALT）途径的肿瘤细胞中，C 丰富的突出端更为普遍，该途径依赖于同源重组（HR）机制。基于瞬时 siRNA 的 HR 特异性蛋白 RAD51、RAD52 和 XRCC3 的耗竭导致 C 突出端水平的变化，表明 5'-C 突出端参与了端粒维持的 HR 依赖性途径。
