Structure of the mammalian ribosome as it decodes the selenocysteine UGA codon.
basic_science · Level V
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- Record sourced from PubMed, PMID 35709277.
- Also identified by DOI 10.1126/science.abg3875 and PMC identifier 10064918.
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Abstract
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<i>S</i> 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<sup>Sec</sup>) 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.
Medical subject headings
- Codon, Terminator
- Peptide Chain Elongation, Translational
- RNA-Binding Proteins
- Ribosomes
- Selenocysteine
- Selenoproteins