THE PROMOTER-PROXIMAL RDNA TERMINATOR AUGMENTS INITIATION BY PREVENTING DISRUPTION OF THE STABLE TRANSCRIPTION COMPLEX CAUSED BY POLYMERASE READ-IN
THE PROMOTER-PROXIMAL RDNA TERMINATOR AUGMENTS INITIATION BY PREVENTING DISRUPTION OF THE STABLE TRANSCRIPTION COMPLEX CAUSED BY POLYMERASE READ-IN
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DOI：
10.1101/gad.3.2.212
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发表时间：
1989-02-01
影响因子：
10.5
通讯作者：
SOLLNERWEBB, B
中科院分区：
文献类型：
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作者：
HENDERSON, SL;RYAN, K;SOLLNERWEBB, B
我们已经研究了小鼠rDNA启动子的转录起始被位于其上游的RNA聚合酶I终止子元件增强的机制。使用终止子元件位于质粒的相对侧而不是启动子附近的模板，或者通过UV诱导的损伤终止质粒中其他地方的转录的条件，我们表明终止子的刺激作用不是位置依赖性的。因此，小鼠终止子元件不会通过先前假定的“通读增强”模型进行刺激，在该模型中，终止的聚合酶在协同反应中被传递到相邻的启动子。终止子的位置独立性和取向依赖性也使得终止子不太可能作为启动子元件或增强子起作用。相反，终止子通过阻止聚合酶在质粒周围完全阅读并从上游通过启动子来增强起始，我们表明这一事件会干扰随后的几轮起始。值得注意的是，这种转录干扰的出现是因为聚合酶穿过启动子破坏了原本稳定的转录复合物，特异性地释放了结合的转录因子D。这些释放的D分子可以与其他模板结合并激活它们的表达。rDNA转录干扰不是由于新聚合酶分子结合的空间位阻，并且它不类似地释放起始能力聚合酶（因子C）。这些研究也令人信服地证明，在体外从rDNA模板分子获得多轮转录。
We have examined the mechanism by which transcriptional initiation at the mouse rDNA promoter is augmented by the RNA polymerase I terminator element that resides just upstream of it. Using templates in which terminator elements are instead positioned at the opposite side of the plasmid rather than proximal to the promoter, or conditions where transcription is terminated elsewhere in the plasmid by UV-induced lesions, we show that the terminator's stimulatory effect is not position dependent. Mouse terminator elements therefore do not stimulate via the previously postulated 'read-through enhancement' model in which terminated polymerases are handed off to an adjacent promoter in a concerted reaction. The position independence and orientation dependence of the terminator also makes it unlikely that the terminator functions as a promoter element or as an enhancer. Instead, terminators serve to augment initiation by preventing polymerases from reading completely around the plasmid and through the promoter from upstream, an event which we show interferes with subsequent rounds of initiation. Notably, this transcriptional interference arises because polymerase passage across a promoter disrupts the otherwise stable transcription complex, specifically releasing the bound transcription factor D. These liberated D molecules can then bind to other templates and activate their expression. The rDNA transcriptional interference is not due to a steric impediment to the binding of new polymerase molecules, and it does not similarly liberate the initiation-competent polymerase (factor C). These studies have also convincingly demonstrated that multiple rounds of transcription are obtained from rDNA template molecules in vitro.