Gene Center and Center for Integrated Protein Science Munich (CIPSM), Department for Chemistry and Biochemistry, University of Munich, Feodor-Lynen-Strasse 25, 81377 Munich, Germany.
Science. 2009 Dec 4;326(5958):1412-5. doi: 10.1126/science.1177662. Epub 2009 Oct 29.
Expression of the Escherichia coli tryptophanase operon depends on ribosome stalling during translation of the upstream TnaC leader peptide, a process for which interactions between the TnaC nascent chain and the ribosomal exit tunnel are critical. We determined a 5.8 angstrom-resolution cryo-electron microscopy and single-particle reconstruction of a ribosome stalled during translation of the tnaC leader gene. The nascent chain was extended within the exit tunnel, making contacts with ribosomal components at distinct sites. Upon stalling, two conserved residues within the peptidyltransferase center adopted conformations that preclude binding of release factors. We propose a model whereby interactions within the tunnel are relayed to the peptidyltransferase center to inhibit translation. Moreover, we show that nascent chains adopt distinct conformations within the ribosomal exit tunnel.
大肠杆菌色氨酸酶操纵子的表达依赖于核糖体在翻译上游 TnaC 前导肽时的停顿，这一过程中 TnaC 新生肽链与核糖体出口隧道之间的相互作用至关重要。我们利用冷冻电镜和单颗粒重构技术，确定了在翻译 tnaC 前导基因时核糖体停顿的分辨率为 5.8 埃的结构。新生肽链在出口隧道内延伸，与核糖体成分在不同的部位接触。在停顿时，肽基转移酶中心内的两个保守残基采用了阻止释放因子结合的构象。我们提出了一个模型，即隧道内的相互作用被传递到肽基转移酶中心，从而抑制翻译。此外，我们还表明，新生肽链在核糖体出口隧道内采用不同的构象。
