Cech T R, Tanner N K, Tinoco I, Weir B R, Zuker M, Perlman P S
Proc Natl Acad Sci U S A. 1983 Jul;80(13):3903-7. doi: 10.1073/pnas.80.13.3903.
Splicing of the ribosomal RNA precursor of Tetrahymena is an autocatalytic reaction, requiring no enzyme or other protein in vitro. The structure of the intervening sequence (IVS) appears to direct the cleavage/ligation reactions involved in pre-rRNA splicing and IVS cyclization. We have probed this structure by treating the linear excised IVS RNA under nondenaturing conditions with various single- and double-strand-specific nucleases and then mapping the cleavage sites by using sequencing gel electrophoresis. A computer program was then used to predict the lowest-free-energy secondary structure consistent with the nuclease cleavage data. The resulting structure is appealing in that the ends of the IVS are in proximity; thus, the IVS can help align the adjacent coding regions (exons) for ligation, and IVS cyclization can occur. The Tetrahymena IVS has several sequences in common with those of fungal mitochondrial mRNA and rRNA IVSs, sequences that by genetic analysis are known to be important cis-acting elements for splicing of the mitochondrial RNAs. In the predicted structure of the Tetrahymena IVS, these sequences interact in a pairwise manner similar to that postulated for the mitochondrial IVSs. These findings suggest a common origin of some nuclear and mitochondrial introns and common elements in the mechanism of their splicing.
嗜热四膜虫核糖体RNA前体的剪接是一种自催化反应，在体外不需要酶或其他蛋白质。间隔序列（IVS）的结构似乎指导了前体rRNA剪接和IVS环化过程中涉及的切割/连接反应。我们通过在非变性条件下用各种单链和双链特异性核酸酶处理线性切除的IVS RNA，然后使用测序凝胶电泳对切割位点进行定位，来探究这种结构。然后使用一个计算机程序预测与核酸酶切割数据一致的最低自由能二级结构。所得结构很吸引人，因为IVS的末端彼此靠近；因此，IVS可以帮助将相邻的编码区（外显子）对齐以便连接，并且IVS环化可以发生。嗜热四膜虫IVS与真菌线粒体mRNA和rRNA的IVS有几个共同序列，通过遗传分析已知这些序列是线粒体RNA剪接的重要顺式作用元件。在嗜热四膜虫IVS的预测结构中，这些序列以类似于线粒体IVS所假定的成对方式相互作用。这些发现表明一些核内含子和线粒体内含子有共同的起源，并且它们的剪接机制中有共同的元件。
