Interaction between the poly(A)-binding protein Pab1 and the eukaryotic release factor eRF3 regulates translation termination but not mRNA decay in Saccharomyces cerevisiae

Eukaryotic release factor 3 (eRF3) is implicated in translation termination and also interacts with the poly(A)-binding protein (PABP, Pab1 in yeast), a major player in mRNA metabolism. Despite conservation of this interaction, its precise function remains elusive. First, we showed experimentally that yeast eRF3 does not contain any obvious consensus PAM2 (PABP-interacting motif 2). Thus, in yeast this association is different from the well described interaction between the metazoan factors. To gain insight into the exact function of this interaction, we then analyzed the phenotypes resulting from deleting the respective binding domains. Deletion of the Pab1 interaction domain on eRF3 did not affect general mRNA stability or nonsense-mediated mRNA decay (NMD) pathway and induced a decrease in translational readthrough. Furthermore, combined deletions of the respective interacting domains on eRF3 and on Pab1 were viable, did not affect Pab1 function in mRNA stability and harbored an antisuppression phenotype. Our results show that in Saccharomyces cerevisiae the role of the Pab1 C-terminal domain in mRNA stability is independent of eRF3 and the association of these two factors negatively regulates translation termination.