Structure of the mammalian ribosome as it decodes the selenocysteine UGA codon.
Hilal, T., Killam, B.Y., Grozdanovic, M., Dobosz-Bartoszek, M., Loerke, J., Burger, J., Mielke, T., Copeland, P.R., Simonovic, M., Spahn, C.M.T.(2022) Science 376: 1338-1343
- PubMed: 35709277 
- DOI: https://doi.org/10.1126/science.abg3875
- Primary Citation of Related Structures:  
7ZJW, 7ZJX - PubMed 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 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.
Organizational Affiliation: 
Institut für Medizinische Physik und Biophysik, Charité-Universitätsmedizin Berlin, 10117 Berlin, Germany.