Kabir Shaheen, Hockemeyer Dirk, de Lange Titia
Laboratory for Cell Biology and Genetics, The Rockefeller University, New York, NY 10065, USA.
Department of Molecular and Cellular Biology, University of California, Berkeley, Berkeley, CA 94720, USA.
Cell Rep. 2014 Nov 20;9(4):1273-80. doi: 10.1016/j.celrep.2014.10.014. Epub 2014 Nov 6.
The conserved protein Rap1 functions at telomeres in fungi, protozoa, and vertebrates. Like yeast Rap1, human Rap1 has been implicated in telomere length regulation and repression of nonhomologous end-joining (NHEJ) at telomeres. However, mouse telomeres lacking Rap1 do not succumb to NHEJ. To determine the functions of human Rap1, we generated several transcription activator-like effector nuclease (TALEN)-mediated human cell lines lacking Rap1. Loss of Rap1 did not affect the other components of shelterin, the modification of telomeric histones, the subnuclear position of telomeres, or the 3' telomeric overhang. Telomeres lacking Rap1 did not show a DNA damage response, NHEJ, or consistent changes in their length, indicating that Rap1 does not have an important function in protection or length regulation of human telomeres. As human Rap1, like its mouse and unicellular orthologs, affects gene expression, we propose that the conservation of Rap1 reflects its role in transcriptional regulation rather than a function at telomeres.
保守蛋白Rap1在真菌、原生动物和脊椎动物的端粒中发挥作用。与酵母Rap1一样，人类Rap1也与端粒长度调节以及端粒处非同源末端连接（NHEJ）的抑制有关。然而，缺乏Rap1的小鼠端粒不会出现NHEJ。为了确定人类Rap1的功能，我们构建了几种由转录激活样效应核酸酶（TALEN）介导的缺乏Rap1的人类细胞系。Rap1的缺失不影响端粒保护蛋白复合体的其他成分、端粒组蛋白的修饰、端粒的亚核位置或3'端粒悬突。缺乏Rap1的端粒未显示出DNA损伤反应、NHEJ或其长度的一致变化，这表明Rap1在人类端粒的保护或长度调节中不具有重要功能。由于人类Rap1与其小鼠和单细胞直系同源物一样会影响基因表达，我们认为Rap1的保守性反映了其在转录调控中的作用，而非在端粒中的功能。
