Peptide-chain elongation during protein synthesis entails sequential aminoacyl-tRNA selection and translocation reactions that proceed rapidly (2–20 per second) and with a low error rate (around 10⁻³ to 10⁻⁵ at each step) over thousands of cycles¹. The cadence and fidelity of ribosome transit through mRNA templates in discrete codon increments is a paradigm for movement in biological systems that must hold for diverse mRNA and tRNA substrates across domains of life. Here we use single-molecule fluorescence methods to guide the capture of structures of early translocation events on the bacterial ribosome. Our findings reveal that the bacterial GTPase elongation factor G specifically engages spontaneously achieved ribosome conformations while in an active, GTP-bound conformation to unlock and initiate peptidyl-tRNA translocation. These findings suggest that processes intrinsic to the pre-translocation ribosome complex can regulate the rate of protein synthesis, and that energy expenditure is used later in the translocation mechanism than previously proposed.

蛋白质合成过程中的肽链延伸需要连续的氨酰-tRNA 选择和易位反应，这些反应在数千个循环中快速进行（每秒 2-20 次）并且错误率低（每步大约 10 ^-3 到 10 ^{-5 ） 1}. 核糖体以离散密码子增量通过 mRNA 模板转运的节奏和保真度是生物系统中运动的范例，它必须适用于跨生命领域的不同 mRNA 和 tRNA 底物。在这里，我们使用单分子荧光方法来指导捕获细菌核糖体早期易位事件的结构。我们的研究结果表明，细菌 GTPase 延伸因子 G 在处于活跃的 GTP 结合构象中时特别参与自发实现的核糖体构象，以解锁和启动肽基-tRNA 易位。这些发现表明，易位前核糖体复合物固有的过程可以调节蛋白质合成的速率，并且能量消耗在易位机制中的使用比以前提出的要晚。