The elongation of eukaryotic selenoproteins relies on a poorly understood process of interpreting in-frame UGA stop codons as selenocysteine (Sec). We used cryo-electron microscopy to visualize Sec UGA recoding in mammals. A complex between the noncoding Sec-insertion sequence (SECIS), SECIS-binding protein 2 (SBP2), and 40 S ribosomal subunit enables Sec-specific elongation factor eEFSec to deliver Sec. eEFSec and SBP2 do not interact directly but rather deploy their carboxyl-terminal domains to engage with the opposite ends of the SECIS. By using its Lys-rich and carboxyl-terminal segments, the ribosomal protein eS31 simultaneously interacts with Sec-specific transfer RNA (tRNA Sec ) and SBP2, which further stabilizes the assembly. eEFSec is indiscriminate toward l -serine and facilitates its misincorporation at Sec UGA codons. Our results support a fundamentally distinct mechanism of Sec UGA recoding in eukaryotes from that in bacteria.

中文翻译：

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哺乳动物核糖体解码硒代半胱氨酸 UGA 密码子的结构


真核含硒蛋白的延伸依赖于将框内 UGA 终止密码子解释为硒代半胱氨酸 (Sec) 的过程，这一过程知之甚少。我们使用冷冻电子显微镜来可视化哺乳动物中的 Sec UGA 重新编码。非编码 Sec 插入序列 (SECIS)、SECIS 结合蛋白 2 (SBP2) 和 40 之间的复合物S核糖体亚基使 Sec 特异性延伸因子 eEFSec 能够提供 Sec。 eEFSec 和 SBP2 不直接相互作用，而是部署它们的羧基末端结构域来与 SECIS 的相对端接合。通过使用其富含赖氨酸和羧基末端的片段，核糖体蛋白 eS31 同时与 Sec 特异性转移 RNA (tRNA) 相互作用秒) 和 SBP2，进一步稳定装配。 eEFSec 不加区别地对待我-丝氨酸并促进其在 Sec UGA 密码子处的错误掺入。我们的结果支持真核生物中的 Sec UGA 重新编码机制与细菌中的机制截然不同。