Excised group II introns in yeast mitochondria are lariats and can be formed by self-splicing in vitro
Excised group II introns in yeast mitochondria are lariats and can be formed by self-splicing in vitro
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DOI：
10.1016/0092-8674(86)90756-7
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发表时间：
1986-01
期刊：
影响因子：
64.5
通讯作者：
R. Veen;A. Arnberg;G. Horst;L. Bonen;Henk F. Tabak;L. Grivell
中科院分区：
文献类型：
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作者：
R. Veen;A. Arnberg;G. Horst;L. Bonen;Henk F. Tabak;L. Grivell
在电镜下，酵母线粒体中切除的II组内含子呈共价闭合的环状。我们发现这些环状分子是分支的，类似于酵母和高等真核生物中核前mrna剪接产生的分枝体。这类内含子中的一个成员（在细胞色素c氧化酶亚基I的基因中占全部%）能够在体外进行自剪接，使外显子-外显子正确连接，并导致被切除的内含子呈现线性和线性形式。后一分子的核酸酶酶切揭示了一个复杂的寡核苷酸的存在，其结构可能为a &，因此类似于核前mrna在剪接体依赖反应中形成的分支点。与I组内含子不同，II组内含子不明显依赖于GTP进行自剪接，并且未观察到孤立的线性内含子的环状化。提出了一个解释这些观测结果的模型。根据核苷酸序列的相似性、阅读框之间的氨基酸同源性以及潜在的RNA二级结构，酵母mtDNA中的内含子可分为两类（Michel和Dujon， 1983）。优势类（I群）的成员广泛存在于其他真菌的mtDNA8中。序列比较以及对剪接缺陷突变体的研究结果表明，内含子折叠在剪接连接的排列中起着重要作用，并鉴定了一系列剪接所需的短序列元件（参见Waring和Davies， 1984年的综述）。四膜虫大rRNA的核编码基因中存在“自剪接”内含子，这一发现也引起了人们对这些内含子及其切除机制的额外兴趣（ceech等，1981；Zaug等，1983）
Excised group II introns in yeast mitochondria appear as covalently closed circles under the electron microscope. We show that these circular molecules are branched and resemble the lariats arising through splicing of nuclear pre-mRNAs In yeast and higher eukaryotes. One member of this intron class (al% in the gene for cytochrome c oxldase subunit I) Is capable of self-splicing in vitro, giving correct exon-exon ligation and resulting in the appearance of both linear and lariat forms of the excised lntron. Nuclease digestion of the latter molecules reveals the presence of a complex oligonucleotide with the probable structure A& which thus resembles the branch point formed in the spliceosome-dependent reactions undergone by nuclear pre-mRNAs. Unlike group I introns, this group II intron is not demonstrably dependent on GTP for selfsplicing and circularization of the isolated, linear intron is not observed. A model accounting for these observations is presented.The introns in yeast mtDNA can be assigned to two classes based on similarities in nucleotide sequence, amino acid homologies between reading frames when present, and potential RNA secondary structure (Michel and Dujon, 1983). Members of the predominant class (group I) are widespread in the mtDNA8 of other fungi. Sequence comparisons, together with the results of studies with splicing-deficient mutants, have led to the proposal that intron folding plays an important role in the alignment of splice junctions, and to the identification of a series of short sequence elements necessary for splicing (see Waring and Davies, 1984, for review). Additional interest in these introns and their mechanism of excision has been aroused by the finding that the “self-splicing” intron present in the nuclear-encoded gene for the large rRNA of Tetrahymena (Cech et al., 1981; Zaug et al., 1983) is also