Eukaryotic ribosome recognizes 3 context and stimulates stop codon readthrough

It is known that the nucleotide context surrounding stop codons significantly affects the efficiency of translation termination. In eukaryotes, various 3' contexts have been described that are unfavourable for translation termination; however, the exact molecular mechanism that mediates their effect remains unknown. In this study, we used a reconstituted mammalian translation system to examine the efficiency of stop codons in different contexts, including several previously described weak 3' stop codon contexts. Our results revealed that ribosomes can independently recognize certain contexts and ignore stop codons that are followed by these sequences. Moreover, the efficiency of translation termination at the weak 3' contexts was almost equal to the one at the standard context. We propose that weak 3' contexts interact with the 18S rRNA provoking a conformational change in the U-turn-like structure of the stop codon in the A site of ribosome. This change makes incorporation of the near-cognate tRNA more preferable than recognition of the stop codon by the release factors and increases readthrough.