Rescuing stalled ribosomes often involves their splitting into subunits. In many bacteria, the resultant large subunits bearing peptidyl-tRNAs are processed by the ribosome-associated quality control (RQC) apparatus that extends the C termini of the incomplete nascent polypeptides with polyalanine tails to facilitate their degradation. Although the tailing mechanism is well established, it is unclear how the nascent polypeptides are cleaved off the tRNAs. We show that peptidyl-tRNA hydrolase (Pth), the known role of which has been to hydrolyze ribosome-free peptidyl-tRNA, acts in concert with RQC factors to release nascent polypeptides from large ribosomal subunits. Dislodging from the ribosomal catalytic center is required for peptidyl-tRNA hydrolysis by Pth. Nascent protein folding may prevent peptidyl-tRNA retraction and interfere with the peptide release. However, oligoalanine tailing makes the peptidyl-tRNA ester bond accessible for Pth-catalyzed hydrolysis. Therefore, the oligoalanine tail serves not only as a degron but also as a facilitator of Pth-catalyzed peptidyl-tRNA hydrolysis.

拯救停滞的核糖体通常涉及将其分裂成亚基。在许多细菌中，产生的带有肽基-tRNA 的大亚基由核糖体相关质量控制 (RQC) 装置处理，该装置用聚丙氨酸尾部延伸不完整的新生多肽的 C 末端，以促进其降解。尽管加尾机制已被充分确立，但尚不清楚新生多肽如何从 tRNA 上裂解下来。我们发现肽基-tRNA 水解酶 (Pth) 的已知作用是水解不含核糖体的肽基-tRNA，它与 RQC 因子协同作用，从大核糖体亚基中释放新生多肽。 Pth 水解肽基-tRNA 需要从核糖体催化中心脱离。新生蛋白折叠可能会阻止肽基-tRNA 收缩并干扰肽释放。然而，寡聚丙氨酸拖尾使得肽基-tRNA 酯键易于发生 Pth 催化的水解。因此，寡聚丙氨酸尾不仅充当降解决定子，而且充当 Pth 催化的肽基-tRNA 水解的促进剂。