Department of Biochemistry and Biophysics, Texas A and M University, 2128 TAMU, College Station, TX 77843-2128, USA.
Proc Natl Acad Sci U S A. 2011 Jan 4;108(1):73-78. doi: 10.1073/pnas.1013021107. Epub 2010 Dec 16.
Telomerase is a ribonucleoprotein (RNP) reverse transcriptase whose essential RNA subunit (TER) functions as a template for telomere repeat synthesis. Here we report the identification of two divergent TER moieties in the flowering plant Arabidopsis thaliana. Although both TER1 and TER2 copurify with telomerase activity and serve as templates for telomerase in vitro, depletion of TER1, but not TER2, leads to decreased telomerase activity and progressive telomere shortening in vivo. Moreover, mutation of the templating domain in TER1 results in the incorporation of mutant telomere repeats on chromosome ends. Thus, TER1 provides the major template for telomerase in vivo. We also show that POT1a binds TER1 with a Kd of 2 × 10(-7) M and the two components assemble into an enzymatically active RNP in vivo. In contrast, TER1-POT1b and TER2-POT1a associations were not observed. In other organisms POT1 proteins bind telomeric DNA and provide chromosome end protection. We propose that duplication of TER and POT1 in Arabidopsis fueled the evolution of novel protein-nucleic acid interactions and the migration of POT1 from the telomere to the telomerase RNP.
端粒酶是一种核糖核蛋白（RNP）逆转录酶，其必需的 RNA 亚基（TER）作为端粒重复合成的模板。在这里，我们报告了在开花植物拟南芥中鉴定出的两个不同的 TER 部分。尽管 TER1 和 TER2 都与端粒酶活性共纯化，并在体外作为端粒酶的模板，但 TER1 的耗竭而不是 TER2 的耗竭导致体内端粒酶活性降低和端粒逐渐缩短。此外，TER1 模板结构域的突变导致染色体末端掺入突变的端粒重复。因此，TER1 为体内端粒酶提供了主要模板。我们还表明，POT1a 以 2×10(-7) M 的 Kd 结合 TER1，并且这两个组件在体内组装成具有酶活性的 RNP。相比之下，未观察到 TER1-POT1b 和 TER2-POT1a 缔合。在其他生物体中，POT1 蛋白结合端粒 DNA 并提供染色体末端保护。我们提出，拟南芥中 TER 和 POT1 的重复推动了新型蛋白-核酸相互作用的进化，以及 POT1 从端粒向端粒酶 RNP 的迁移。
