Group I-like ribozymes with a novel core organization perform obligate sequential hydrolytic cleavages at two processing sites
Group I-like ribozymes with a novel core organization perform obligate sequential hydrolytic cleavages at two processing sites
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DOI：
10.1017/s1355838298971758
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发表时间：
1998-05-01
期刊：
影响因子：
4.5
通讯作者：
Johansen, S
中科院分区：
文献类型：
--
作者：
Einvik, C;Nielsen, H;Johansen, S
在真核微生物Didymium和Naegleria中发现了一类新的具有保守结构组织和功能的自我剪接I组内含子。这些复杂的rDNA内含子包含两个不同的核酶具有不同的功能：一个定期组I剪接核酶和一个小的内部组I样核酶（GIR 1），可能参与蛋白质的表达。发现GIR 1在两个内部位点以专性顺序切割。两个位点都位于催化核心的3'。GIR 1催化的酯交换反应不能被检测到。我们已经比较了所有可用的GIR 1序列，并提出了一个共同的RNA二级结构类似的组I剪接核酶，但有一些重要的差异。GIR 1缺乏大多数外围序列组分，以及P1片段，并且在大约160-190 nt处，它们是自然界已知的最小的功能组I核酶。所有的GIR 1 s被发现包含一个新的6-bp的假结（P15）在其催化核心区域。通过RNA结构探测和定点突变从Didymium GIR 1获得了所提出结构的实验支持。三维建模表明，在两个主要结构域P3-P8和P4-P6之间的裂缝中暴露有功能必需的P15的复合折叠核酶。
A new category of self-splicing group I introns with conserved structural organization and function is found among the eukaryotic microorganisms Didymium and Naegleria. These complex rDNA introns contain two distinct ribozymes with different functions: a regular group I splicing-ribozyme and a small internal group I-like ribozyme (GIR1), probably involved in protein expression. GIR1 was found to cleave at two internal sites in an obligate sequential order. Both sites are located 3' of the catalytic core. GIR1-catalyzed transesterification reactions could not be detected. We have compared all available GIR1 sequences and propose a common RNA secondary structure resembling that of group I splicing-ribozymes, but with some important differences. The GIR1s lack most peripheral sequence components, as well as a P1 segment, and, at approximately 160-190 nt, they are the smallest functional group I ribozymes known from nature. All GIR1s were found to contain a novel 6-bp pseudoknot (P15) within their catalytic core region. Experimental support of the proposed structure was obtained from the Didymium GIR1 by RNA structure probing and site-directed mutagenesis, Three-dimensional modeling indicates a compactly folded ribozyme with the functionally essential P15 exposed in the cleft between the two principal domains P3-P8 and P4-P6.