Boric acid intercepts 80S ribosome migration from AUG-stop by stabilizing eRF1 at the A site

In response to environmental changes, cells flexibly and rapidly alter gene expression, through translational controls. In plants, the translation of NIP5;1, a boric acid diffusion facilitator, is upregulated through upstream open reading frames (uORFs) that comprise only AUG and stop codons, in response to a shortage of boric acid in the environment. However, the molecular details of how the minimum uORF controls the translation of the downstream main ORF, in a boric acid concentration-dependent manner, have remained unclear. Here, combining ribosome profiling, TCP-Seq, structural analysis with cryo-electron microscopy, and biochemical assays, we showed that the 80S ribosome (80S) assembled at AUG-stop migrates into the subsequent RNA segment, followed by downstream translation initiation, and that boric acid impedes this process by the stable confinement of eukaryotic release factor 1 (eRF1) on the 80S on AUG-stop. Our results provide molecular insight into translation regulation by a minimum and environment-responsive uORF. Translation complex profile sequencing (TCP-seq)

细胞可通过翻译调控机制，灵活且快速地调整基因表达水平以响应环境变化。在植物中，当环境中硼酸匮乏时，仅包含AUG与终止密码子的上游开放阅读框（upstream open reading frames，uORFs）可上调硼酸扩散协助因子NIP5;1的翻译过程。然而，此类极简uORF如何以硼酸浓度依赖的方式调控下游主开放阅读框（main ORF）的翻译过程，其分子细节至今仍未阐明。本研究结合核糖体图谱技术、翻译复合物谱测序（Translation complex profile sequencing，TCP-seq）、冷冻电子显微镜结构分析与生化实验，证实：在AUG-终止密码子位点组装的80S核糖体（80S）会迁移至后续RNA区段，随后启动下游翻译起始；而硼酸可通过将真核释放因子1（eukaryotic release factor 1，eRF1）稳定束缚在AUG-终止密码子位点的80S核糖体上，阻碍这一过程。本研究结果为兼具极简特征与环境响应性的uORF介导的翻译调控机制提供了分子层面的认知。