While translation initiation is extensively regulated, fewer mechanisms are known to control translation elongation. We discovered that prolonged stimulation of macrophages leads to suppression of protein synthesis at the level of translation elongation, through pausing of ribosomes on the first 20 codons of mRNA open reading frames. Early elongation pausing results from ubiquitination of the translation machinery including the translation initiation factor eIF3m. We demonstrate that eIF3m is required for efficient early elongation in unstimulated macrophages. The mechanism is of general nature, since eIF3m and ubiquitination control early elongation pausing also in cells outside of the immune system. This work uncovers early elongation as a critical phase during which polypeptide synthesis is actively controlled.

Murine macrophage cell line Raw264.7 was treated with LPS for 16 h and proteome wide changes in ubiquitination levels were assessed by mass spectrometry using enrichment of di-glycine-modified peptides.