Waring R B, Scazzocchio C, Brown T A, Davies R W
J Mol Biol. 1983 Jul 5;167(3):595-605. doi: 10.1016/s0022-2836(83)80100-4.
We present the first indication of a direct relationship between a nuclear and a mitochondrial splicing system. The intron in the precursor of the large, nuclearly coded ribosomal RNA of two species of Tetrahymena possesses all the features of a class of fungal mitochondrial introns. Sequences conserved in mitochondrial introns of different fungal species are also found in the same order in these Tetrahymena nuclear introns, and the intron RNA can be folded to form a secondary structure similar to that proposed for mitochondrial introns by Davies et al. (1982). This "core" secondary structure brings the ends of the intron together. Furthermore, the first intron in the precursor of the large, nuclearly coded rRNA of Physarum polycephalum also has the characteristic conserved sequences and core RNA secondary structure. The limited sequence data available suggest that the intron in the large rRNA of chloroplasts in Chlamydomonas reinhardtii also resembles the mitochondrial introns. Tetrahymena large nuclear rRNA introns also have an internal sequence that can act as an adaptor by pairing with upstream and downstream exon sequences adjacent to the splice junctions to precisely align the splice junctions. These nuclear introns therefore fit the model of the role of intron RNA in the splicing process that was proposed by Davies et al. (1982), suggesting that the mechanisms of splicing may be very similar in these apparently diverse systems. It is therefore probable that the RNA secondary structures for which there is good evidence in the case of mitochondrial introns will be found to form the basis of active site structure and precise alignment in splicing and cyclization of the Tetrahymena intron "ribozyme".
我们首次表明了细胞核与线粒体剪接系统之间存在直接关系。两种四膜虫的大型细胞核编码核糖体RNA前体中的内含子具有一类真菌线粒体内含子的所有特征。在不同真菌物种的线粒体内含子中保守的序列，在这些四膜虫细胞核内含子中也按相同顺序被发现，并且内含子RNA可以折叠形成类似于戴维斯等人（1982年）提出的线粒体内含子的二级结构。这种“核心”二级结构使内含子的两端聚集在一起。此外，多头绒泡菌的大型细胞核编码rRNA前体中的第一个内含子也具有特征性的保守序列和核心RNA二级结构。现有的有限序列数据表明，莱茵衣藻叶绿体大rRNA中的内含子也类似于线粒体内含子。四膜虫大型细胞核rRNA内含子还有一个内部序列，它可以通过与剪接连接处相邻的上游和下游外显子序列配对来充当衔接子，从而精确对齐剪接连接处。因此，这些细胞核内含子符合戴维斯等人（1982年）提出的内含子RNA在剪接过程中作用的模型，这表明在这些明显不同的系统中剪接机制可能非常相似。因此，很可能会发现，在线粒体内含子中已有充分证据的RNA二级结构将构成四膜虫内含子“核酶”剪接和环化中活性位点结构及精确对齐的基础。
