Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138, USA.
Proc Natl Acad Sci U S A. 2011 Dec 20;108(51):20339-44. doi: 10.1073/pnas.1017686108. Epub 2011 May 13.
Telomerase ribonucleoprotein (RNP) employs an RNA subunit to template the addition of telomeric repeats onto chromosome ends. Previous studies have suggested that a region of the RNA downstream of the template may be important for telomerase activity and that the region could fold into a pseudoknot. Whether the pseudoknot motif is formed in the active telomerase RNP and what its functional role is have not yet been conclusively established. Using single-molecule FRET, we show that the isolated pseudoknot sequence stably folds into a pseudoknot. However, in the context of the full-length telomerase RNA, interference by other parts of the RNA prevents the formation of the pseudoknot. The protein subunits of the telomerase holoenzyme counteract RNA-induced misfolding and allow a significant fraction of the RNPs to form the pseudoknot structure. Only those RNP complexes containing a properly folded pseudoknot are catalytically active. These results not only demonstrate the functional importance of the pseudoknot but also reveal the critical role played by telomerase proteins in pseudoknot folding.
端粒酶核糖核蛋白（RNP）利用 RNA 亚基将端粒重复序列模板添加到染色体末端。先前的研究表明，模板下游的 RNA 区域可能对端粒酶活性很重要，并且该区域可能折叠成假结。假结模体是否在活性端粒酶 RNP 中形成，以及它的功能作用尚未得到明确证实。使用单分子 FRET，我们表明分离的假结序列稳定地折叠成假结。然而，在全长端粒酶 RNA 的背景下，RNA 的其他部分的干扰阻止了假结的形成。端粒酶全酶的蛋白质亚基可对抗 RNA 诱导的错误折叠，并使大量 RNP 形成假结结构。只有那些包含正确折叠假结的 RNP 复合物才具有催化活性。这些结果不仅证明了假结的功能重要性，而且还揭示了端粒酶蛋白在假结折叠中发挥的关键作用。
