Dedicated chaperone at the ribosome safeguards the proteostasis network during eEF1A biogenesis

Cotranslational protein folding depends on general chaperones that engage highly diverse nascent chains at the ribosomes. Here we find that the universal cotranslational machinery adapts to accommodate the challenging biogenesis of abundantly expressed eukaryotic translation elongation factor 1A (eEF1A). During eEF1A synthesis, chaperone Chp1 is recruited to the ribosome with the help of the nascent polypeptide-associated complex (NAC), where it safeguards eEF1A biogenesis. Aberrant eEF1A production triggers instant proteolysis, widespread protein aggregation, activation of Hsf1 stress transcription and compromises cellular fitness. The expression of pathogenic eEF1A2 variants linked to epileptic-dyskinetic encephalopathy is protected by Chp1. Thus, eEF1A is a difficult to fold protein that necessitates dedicated folding factor Chp1 at the ribosomal tunnel exit to protect the eukaryotic cell from proteostasis collapse. Overall design: Selective Ribosome Profiling of Chp1 in S. cerevisiae (BY4741 Chp1-GFP strain, performed in two replicates, each consisting of an IP sample and a corresponding total translatome sample. As a negative control, IP and total translatome samples were prepared in WT untagged BY4741 cells also in two replicates). Ribosome profiling in S. cerevisiae (BY4741 WT or Chp1? cells, total translatomes in two replicates each)