Department of Molecular Biosciences, Northwestern University, Evanston, IL, USA.
Wiley Interdiscip Rev RNA. 2013 Sep-Oct;4(5):507-22. doi: 10.1002/wrna.1175. Epub 2013 Jun 10.
The T-loop is a frequently occurring five-nucleotide motif found in the structure of noncoding RNAs where it is commonly assumed to play an important role in stabilizing the tertiary RNA structure by facilitating long-range interactions between different regions of the molecule. T-loops were first identified in tRNA(Phe) and a formal consensus sequence for this motif was formulated and later revised based on analyses of the crystal structures of prokaryotic ribosomal RNAs and RNase P and the corresponding primary sequence of their orthologues. In the past decade, several new structures of large RNA molecules have been added to the RCSB Protein Data Bank, including the eukaryotic ribosome, a self-splicing group II intron, numerous synthetases in complex with their cognate transfer RNAs (tRNAs), transfer-messenger RNA (tmRNA) in complex with SmpB, several riboswitches, and a complex of bacterial RNase P bound to its tRNA substrate. In this review, the search for T-loops is extended to these new RNA molecules based on the previously established structure-based criteria. The review highlights and discusses the function and additional roles of T-loops in four broad categories of RNA molecules, namely tRNAs, ribosomal RNAs (rRNAs), P RNAs, and RNA genetic elements. Additionally, the potential application for T-loops as interaction modules is also discussed.
T 环是一种在非编码 RNA 结构中经常出现的五核苷酸基序，通常假定它通过促进分子不同区域之间的长程相互作用，在稳定三级 RNA 结构中发挥重要作用。T 环最初在 tRNA(Phe)中被鉴定出来，并且针对该基序制定了正式的共识序列，并根据原核核糖体 RNA 和 RNase P 的晶体结构以及它们的同源物的相应原始序列的分析进行了后续修订。在过去的十年中，已经向 RCSB 蛋白质数据库中添加了几种新的大 RNA 分子结构，包括真核核糖体、自我剪接的 II 类内含子、与它们同源的转移 RNA(tRNA)复合的众多合成酶、与 SmpB 复合的转移信使 RNA(tmRNA)、几种核糖开关和与 tRNA 底物结合的细菌 RNase P 复合物。在本综述中，基于先前建立的基于结构的标准，将 T 环的搜索扩展到这些新的 RNA 分子。本综述突出并讨论了 T 环在四类 RNA 分子（tRNA、核糖体 RNA(rRNA)、P RNA 和 RNA 遗传元件）中的功能和其他作用。此外，还讨论了 T 环作为相互作用模块的潜在应用。
