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首页> 外文期刊>Journal of Molecular Biology >The presence of an RNA:DNA hybrid that is prone to slippage promotes termination by T7 RNA polymerase
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The presence of an RNA:DNA hybrid that is prone to slippage promotes termination by T7 RNA polymerase

机译：存在易于滑动的RNA：DNA杂合体的存在会促进T7 RNA聚合酶的终止

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摘要

Intrinsic termination signals for multisubunit bacterial RNA polymerases (RNAPs) encode a GC-rich stem-loop structure followed by a polyuridine [poly(U)] tract, and it has been proposed that steric clash of the stem-loop with the exit pore of the RNAP imposes a shearing force on the RNA in the downstream RNA:DNA hybrid, resulting in misalignment of the active site. The structurally unrelated T7 RNAP terminates at a similar type of signal (TΦ), suggesting a common mechanism for termination. In the absence of a hairpin (passive conditions), T7 RNAP slips efficiently in both homopolymeric A and U tracts, and we have found that replacement of the U tract in TΦ with a slippage-prone A tract still allows efficient termination. Under passive conditions, incorporation of a single G residue following a poly(U) tract (which is the situation during termination at TΦ) results in a "locked" complex that is unable to extend the transcript. Our results support a model in which transmission of the shearing force generated by steric clash of the hairpin with the exit pore is promoted by the presence of a slippery tracts downstream, resulting in alterations in the active site and the formation of a locked complex that represents an early step in the termination pathway.
机译：多亚基细菌RNA聚合酶（RNAPs）的内在终止信号编码富含GC的茎环结构，随后是聚尿苷[poly（U）]束，并且有人提出，茎环的空间冲突与RNAP对下游RNA：DNA杂种中的RNA施加剪切力，导致活性位点错位。结构上不相关的T7 RNAP终止于相似类型的信号（TΦ），这提示了终止的通用机制。在没有发夹的情况下（被动条件），T7 RNAP在均聚物A和U束中均有效滑动，我们发现用易滑的A束替换TΦ中的U束仍可有效终止。在被动条件下，在聚（U）序列后引入单个G残基（这是在TΦ终止时的情况）会导致无法扩展转录本的“锁定”复合物。我们的结果支持了一个模型，在该模型中，发夹与出口孔的空间碰撞产生的剪切力的传递通过下游滑道的存在而得以促进，从而导致活性部位发生改变并形成了代表终止途径的早期步骤。

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