Wu M, Tinoco I
Department of Chemistry, University of California, Berkeley, and Structural Biology Department, Lawrence Berkeley National Laboratory, Berkeley, CA 94720-1460, USA.
Proc Natl Acad Sci U S A. 1998 Sep 29;95(20):11555-60. doi: 10.1073/pnas.95.20.11555.
The secondary structure of the P5abc subdomain (a 56-nt RNA) of the Tetrahymena thermophila group I intron ribozyme has been determined by NMR. Its base pairing in aqueous solution in the absence of magnesium ions is significantly different from the RNA in a crystal but is consistent with thermodynamic predictions. On addition of magnesium ions, the RNA folds into a tertiary structure with greatly changed base pairing consistent with the crystal structure: three Watson-Crick base pairs, three G.U base pairs, and an extra-stable tetraloop are lost. The common assumption that RNA folds by first forming secondary structure and then forming tertiary interactions from the unpaired bases is not always correct.
嗜热四膜虫I组内含子核酶的P5abc亚结构域（一种56个核苷酸的RNA）的二级结构已通过核磁共振确定。在没有镁离子的水溶液中，其碱基配对与晶体中的RNA有显著差异，但与热力学预测一致。加入镁离子后，RNA折叠成三级结构，碱基配对发生了很大变化，与晶体结构一致：三个沃森-克里克碱基对、三个G·U碱基对和一个超稳定四环消失。RNA先形成二级结构，然后从不配对的碱基形成三级相互作用的常见假设并不总是正确的。
