Bhattacharyya A, Blackburn E H
Department of Microbiology and Immunology, University of California, San Francisco 94143.
EMBO J. 1994 Dec 1;13(23):5721-31. doi: 10.1002/j.1460-2075.1994.tb06910.x.
Telomerase, an essential ribonucleoprotein reverse transcriptase, adds telomeric DNA to the ends of eukaryotic chromosomes. We examined the conformational properties of the naked RNA moiety of telomerase from two related ciliates, Tetrahymena thermophila and Glaucoma chattoni. As well as finding evidence for features proposed previously on the basis of phylogenetic comparisons, novel conserved structural properties were revealed. Specifically, although the region around helix III was previously proposed to form a pseudoknot, our results indicate that in the naked RNA this region maintains a level of 'plasticity', probably in an equilibrium favoring one of two helices. In addition, these studies reveal that the templating domain is not entirely single-stranded as previously proposed, but is ordered due to constraints imposed by other parts of the RNA. Finally, our results suggest that the GA bulge in helix IV may introduce a structurally conserved kink. We now propose a 'two-domain' structure for the telomerase RNA based on function: one conformationally flexible domain, which includes the template and the region around helix III, involved with enzymatic function, and a second largely helical domain, including helices I and IV and the proposed kink, which may serve as a scaffold for protein binding.
端粒酶是一种必需的核糖核蛋白逆转录酶，它将端粒DNA添加到真核染色体的末端。我们研究了来自两种相关纤毛虫——嗜热四膜虫和恰氏青光眼虫的端粒酶裸RNA部分的构象特性。除了发现基于系统发育比较先前提出的特征的证据外，还揭示了新的保守结构特性。具体而言，虽然先前有人提出螺旋III周围的区域会形成假结，但我们的结果表明，在裸RNA中，该区域保持一定程度的“可塑性”，可能处于有利于两个螺旋之一的平衡状态。此外，这些研究表明，模板结构域并不像先前提出的那样完全是单链的，而是由于RNA其他部分施加的限制而有序排列。最后，我们的结果表明，螺旋IV中的GA凸起可能会引入一个结构保守的扭结。我们现在基于功能为端粒酶RNA提出一种“双结构域”结构：一个构象灵活的结构域，包括模板和螺旋III周围的区域，与酶功能有关；另一个主要是螺旋结构域，包括螺旋I和IV以及提出的扭结，它可能作为蛋白质结合的支架。
