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Tertiary contacts control switching of the SAM-I riboswitch

机译:第三接触控制SAM-I核糖开关的开关

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摘要

Riboswitches are non-coding RNAs that control gene expression by sensing small molecules through changes in secondary structure. While secondary structure and ligand interactions are thought to control switching, the exact mechanism of control is unknown. Using a novel two-piece assay that competes the anti-terminator against the aptamer, we directly monitor the process of switching. We find that the stabilization of key tertiary contacts controls both aptamer domain collapse and the switching of the SAM-I riboswitch from the aptamer to the expression platform conformation. Our experiments demonstrate that SAM binding induces structural alterations that indirectly stabilize the aptamer domain, preventing switching toward the expression platform conformer. These results, combined with a variety of structural probing experiments performed in this study, show that the collapse and stabilization of the aptamer domain are cooperative, relying on the sum of key tertiary contacts and the bimodal stability of the kink-turn motif for function. Here, ligand binding serves to shift the equilibrium of aptamer domain structures from a more open toward a more stable collapsed form by stabilizing tertiary interactions. Our data show that the thermodynamic landscape for riboswitch operation is finely balanced to allow large conformational rearrangements to be controlled by small molecule interactions.
机译:核糖开关是非编码RNA,可通过二级结构的变化来感知小分子,从而控制基因表达。虽然认为二级结构和配体相互作用可控制切换,但确切的控制机制尚不清楚。使用一种新颖的两件式检测技术,该检测试剂可将抗终止剂与适体竞争,我们可以直接监测转换过程。我们发现关键的第三级联系人的稳定控制适体域崩溃和SAM-1核糖开关从适体到表达平台构象的切换。我们的实验表明,SAM结合诱导了结构改变,从而间接稳定了适体结构域,从而阻止了向表达平台构象异构体的转换。这些结果,结合本研究中进行的各种结构探测实验,表明适体结构域的塌陷和稳定是协同的,依赖于关键三级接触的总和扭结转角基序的双峰稳定性发挥功能。在此,配体结合用于通过稳定第三级相互作用来将适体结构域结构的平衡从更开放变为更稳定的折叠形式。我们的数据表明,核糖开关操作的热力学态势很好地平衡,可以通过小分子相互作用来控制大的构象重排。

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