Epshtein Vitaly, Cardinale Christopher J, Ruckenstein Andrei E, Borukhov Sergei, Nudler Evgeny
Department of Biochemistry, New York University School of Medicine, New York, NY 10016, USA.
Mol Cell. 2007 Dec 28;28(6):991-1001. doi: 10.1016/j.molcel.2007.10.011.
Transcription termination signals in bacteria occur in RNA as a strong hairpin followed by a stretch of U residues at the 3' terminus. To release the transcript, RNA polymerase (RNAP) is thought to translocate forward without RNA synthesis. Here we provide genetic and biochemical evidence supporting an alternative model in which extensive conformational changes across the enzyme lead to termination without forward translocation. In this model, flexible parts of the RNA exit channel (zipper, flap, and zinc finger) assist the initial step of hairpin folding (nucleation). The hairpin then invades the RNAP main channel, causing RNA:DNA hybrid melting, structural changes of the catalytic site, and DNA-clamp opening induced by interaction with the G(trigger)-loop. Our results envision the elongation complex as a flexible structure, not a rigid body, and establish basic principles of the termination pathway that are likely to be universal in prokaryotic and eukaryotic systems.
细菌中的转录终止信号在RNA中以一个强发夹结构出现，随后在3'末端有一段U残基序列。为了释放转录本，RNA聚合酶（RNAP）被认为是在没有RNA合成的情况下向前移位。在这里，我们提供了遗传和生化证据，支持一种替代模型，即酶上广泛的构象变化导致终止而无需向前移位。在这个模型中，RNA出口通道的柔性部分（拉链、襟翼和锌指）协助发夹折叠的初始步骤（成核）。然后发夹侵入RNAP主通道，导致RNA:DNA杂交双链解链、催化位点的结构变化以及与G（触发）环相互作用诱导的DNA夹打开。我们的结果设想延伸复合物是一个柔性结构，而不是刚体，并确立了终止途径的基本原理，这些原理可能在原核和真核系统中普遍适用。
