Crystal structure of a group I intron splicing intermediate
Crystal structure of a group I intron splicing intermediate
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DOI：
10.1261/rna.7140504
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发表时间：
2004-12-01
期刊：
影响因子：
4.5
通讯作者：
Strobel, SA
中科院分区：
文献类型：
--
作者：
Adams, PL;Stahley, MR;Strobel, SA
最近报道的一个完整的细菌组I自我剪接内含子与其两个外显子复合的晶体结构提供了第一个RNA剪接机制的分子视角。这种内含子结构，它被困在外显子连接反应之前的状态，也揭示了一个复杂的RNA折叠的架构。大多数内含子包含在三个内部堆叠但序列不连续的螺旋结构域中。在这里的三级氢键和堆叠域之间的相互作用，和单链连接器的部分，它们之间的桥梁，得到充分的描述。该结构的特征包括：（1）在分子的纵向中点处围绕分子的假结带;（2）在结构的外围边缘处的两个四环-四环受体基序;（3）P6-J6/6a和P3-J3/4之间有一个广泛的小沟三联体，它提供了内含子的两个主要结构域之间的主要相互作用界面（P4-P6和P3-P9.0）;（4）采用p形结构并通过活性位点扭转的六核苷酸J8/7单链元件，与所有三个螺旋结构域形成关键接触;和（5）广泛的碱基堆积结构，其实现了所有可能的堆积相互作用的90%。内含子结构进行了验证，羟基自由基足迹法，实验和预测的溶剂可及性之间观察到强相关性。模型的前第一和前第二步骤的内含子剪接提出了与全尺寸的tRNA外显子。他们认为，在两个剪接步骤之间，tRNA相对于内含子经历了相当大的角运动。
A recently reported crystal structure of an intact bacterial group I self-splicing intron in complex with both its exons provided the first molecular view into the mechanism of RNA splicing. This intron structure, which was trapped in the state prior to the exon ligation reaction, also reveals the architecture of a complex RNA fold. The majority of the intron is contained within three internally stacked, but sequence discontinuous, helical domains. Here the tertiary hydrogen bonding and stacking interactions between the domains, and the single-stranded joiner segments that bridge between them, are fully described. Features of the structure include: (1) A pseudoknot belt that circumscribes the molecule at its longitudinal midpoint; (2) two tetraloop-tetraloop receptor motifs at the peripheral edges of the structure; (3) an extensive minor groove triplex between the paired and joiner segments, P6-J6/6a and P3-J3/4, which provides the major interaction interface between the intron's two primary domains (P4-P6 and P3-P9.0); (4) a six-nucleotide J8/7 single stranded element that adopts a p-shaped structure and twists through the active site, making critical contacts to all three helical domains; and (5) an extensive base stacking architecture that realizes 90% of all possible stacking interactions. The intron structure was validated by hydroxyl radical footprinting, where strong correlation was observed between experimental and predicted solvent accessibility. Models of the pre-first and pre-second steps of intron splicing are proposed with full-sized tRNA exons. They suggest that the tRNA undergoes substantial angular motion relative to the intron between the two steps of splicing.