Translation termination involves release factors RF1, RF2 and the GTPase RF3 that recycles RF1 and RF2 from the ribosome. RF3 dissociates from the ribosome in the GDP-bound form and must then exchange GDP for GTP. The 70S ribosome termination complex (70S-TC) accelerates GDP exchange in RF3, suggesting that the 70S-TC can function as the guanine nucleotide exchange factor for RF3. Here, we use cryogenic-electron microscopy to elucidate the mechanism of GDP dissociation from RF3 catalyzed by the Escherichia coli 70S-TC. The non-rotated ribosome bound to RF1 remodels RF3 and induces a peptide flip in the phosphate-binding loop, efficiently ejecting GDP. Binding of GTP allows RF3 to dock at the GTPase center, promoting the dissociation of RF1 from the ribosome. The structures recapitulate the functional cycle of RF3 on the ribosome and uncover the mechanism by which the 70S-TC allosterically dismantles the phosphate-binding groove in RF3, a previously overlooked function of the ribosome.

翻译终止涉及释放因子 RF1、RF2 和从核糖体中回收 RF1 和 RF2 的 GTP 酶 RF3。RF3 以 GDP 结合形式从核糖体上解离，然后必须将 GDP 交换为 GTP。70S 核糖体终止复合物 （70S-TC） 加速了 RF3 中的 GDP 交换，表明 70S-TC 可以作为 RF3 的鸟嘌呤核苷酸交换因子。在这里，我们使用低温电子显微镜阐明了大肠杆菌 70S-TC 催化的 GDP 与 RF3 解离的机制。与 RF1 结合的非旋转核糖体重塑 RF3 并在磷酸盐结合环中诱导肽翻转，从而有效地喷射 GDP。GTP 的结合允许 RF3 停靠在 GTP 酶中心，促进 RF1 与核糖体的解离。这些结构概括了 RF3 在核糖体上的功能循环，并揭示了 70S-TC 变构拆除 RF3 中的磷酸盐结合槽的机制，这是以前被忽视的核糖体功能。