Proteasomal degradation of human release factor eRF3a regulates translation termination complex formation

In eukaryotes, eRF1 and eRF3 are associated in a complex that mediates translation termination. The regulation of the formation of this complex in vivo is far from being understood. In mammalian cells, depletion of eRF3a causes a reduction of eRF1 level by decreasing its stability. Here, we investigate the status of eRF3a when not associated with eRF1. We show that eRF3a forms altered in their eRF1-binding site have a decreased stability, which increases upon cell treatment with the proteasome inhibitor MG132. We also show that eRF3a forms altered in eRF1 binding as well as wild-type eRF3a are polyubiquitinated. These results indicate that eRF3a is degraded by the proteasome when not associated with eRF1 and suggest that proteasomal degradation of eRF3a controls translation termination complex formation by adjusting the eRF3a level to that of eRF1.