In all branches of life, stalled translation intermediates are recognized and processed by ribosome-associated quality control (RQC) pathways. RQC begins with the splitting of stalled ribosomes, leaving an unfinished polypeptide still attached to the large subunit. Ancient and conserved NEMF family RQC proteins target these incomplete proteins for degradation by the addition of C-terminal “tails.” How such tailing can occur without the regular suite of translational components is, however, unclear. Using single-particle cryo-electron microscopy (EM) of native complexes, we show that C-terminal tailing in Bacillus subtilis is mediated by NEMF protein RqcH in concert with RqcP, an Hsp15 family protein. Our structures reveal how these factors mediate tRNA movement across the ribosomal 50S subunit to synthesize polypeptides in the absence of mRNA or the small subunit.

在生活的所有分支中，停滞的翻译中间体均通过核糖体相关的质量控制（RQC）途径识别和处理。RQC从停滞的核糖体分裂开始，剩下未完成的多肽仍附着在大亚基上。古老而保守的NEMF家族RQC蛋白通过添加C末端“尾巴”来靶向这些不完全的蛋白进行降解。但是，尚不清楚在没有常规翻译组件的情况下如何发生这种拖尾现象。使用天然复合物的单粒子冷冻电子显微镜（EM），我们显示枯草芽孢杆菌的C末端拖尾它是由NEMF蛋白RqcH与Hsp15家族蛋白RqcP共同介导的。我们的结构揭示了这些因素如何在不存在mRNA或小亚基的情况下介导tRNA在核糖体50S亚基上的运动以合成多肽。