The CCC Proline Codon Preceding a Stop Codon Modulates Translation Termination in Eukaryotes Depending on the Molecular Context

In bacteria, glycine and proline codons located upstream of stop codons suppress translation termination. However, the effects of these codons in eukaryotes have not been systematically studied. This work demonstrates that the CCC codon of proline preceding a stop codon slows down eukaryotic translation termination when synthesizing a long protein. On the contrary, when synthesizing a short peptide, the proline codon in this position stimulates the formation of termination complexes. Additionally, the role of one of the main regulators of eukaryotic translation termination, the poly(A)-binding protein (PABP), which binds to the poly(A) tail of mRNA, was described in the modulation of translation termination by the 5'-context of the stop codon. It was found that during the synthesis of a short peptide, PABP reduces the dependence of translation termination on the influence of the 5'-contexts of stop codons, while during the synthesis of a long protein, it stimulates translation termination regardless of the 5'-context of the stop codon.