Laboratory for Cell Biology and Genetics, The Rockefeller University, New York, New York, USA.
Mol Cell Biol. 2014 Apr;34(7):1349-62. doi: 10.1128/MCB.01052-13. Epub 2014 Jan 27.
The shelterin protein TIN2 is required for the telomeric accumulation of TPP1/POT1 heterodimers and for the protection of telomeres by the POT1 proteins (POT1a and POT1b in the mouse). TIN2 also binds to TRF1 and TRF2, improving the telomeric localization of TRF2 and its function. Here, we ask whether TIN2 needs to interact with both TRF1 and TRF2 to mediate the telomere protection afforded by TRF2 and POT1a/b. Using a TIN2 allele deficient in TRF1 binding (TIN2-L247E), we demonstrate that TRF1 is required for optimal recruitment of TIN2 to telomeres and document phenotypes associated with the TIN2-L247E allele that are explained by insufficient TIN2 loading onto telomeres. To bypass the requirement for TRF1-dependent recruitment, we fused TIN2-L247E to the TRF2-interacting (RCT) domain of Rap1. The RCT-TIN2-L247E fusion showed improved telomeric localization and was fully functional in terms of chromosome end protection by TRF2, TPP1/POT1a, and TPP1/POT1b. These data indicate that when sufficient TIN2 is loaded onto telomeres, its interaction with TRF1 is not required to mediate the function of TRF2 and the TPP1/POT1 heterodimers. We therefore conclude that shelterin can protect chromosome ends as a TRF2-tethered TIN2/TPP1/POT1 complex that lacks a physical connection to TRF1.
遮蔽蛋白 TIN2 对于端粒中 TPP1/POT1 异二聚体的积累以及 POT1 蛋白(小鼠中的 POT1a 和 POT1b)对端粒的保护是必需的。TIN2 还与 TRF1 和 TRF2 结合,改善了 TRF2 的端粒定位及其功能。在这里,我们想知道 TIN2 是否需要与 TRF1 和 TRF2 相互作用,以介导 TRF2 和 POT1a/b 提供的端粒保护。我们使用一种缺乏与 TRF1 结合的 TIN2 等位基因(TIN2-L247E),证明 TRF1 是 TIN2 最佳招募到端粒所必需的,并记录了与 TIN2-L247E 等位基因相关的表型,这些表型可以通过端粒上 TIN2 负载不足来解释。为了绕过对 TRF1 依赖性募集的需求,我们将 TIN2-L247E 融合到 Rap1 的 TRF2 相互作用(RCT)结构域。RCT-TIN2-L247E 融合显示出改善的端粒定位,并且在 TRF2、TPP1/POT1a 和 TPP1/POT1b 保护染色体末端方面完全功能。这些数据表明,当足够的 TIN2 加载到端粒上时,其与 TRF1 的相互作用不是介导 TRF2 和 TPP1/POT1 异二聚体功能所必需的。因此,我们得出结论,遮蔽蛋白可以作为缺乏与 TRF1 物理连接的 TRF2 连接的 TIN2/TPP1/POT1 复合物来保护染色体末端。
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