Translation fidelity mechanisms and their changes in aging.

Protein errors (amino acid misincorporations) are associated to protein misfolding and misfunction, and lower levels correlate with longer lifespan 1 . Despite their prevalence, proteome-wide tracking of misincorporations in eukaryotes is challenging, with most insights being recent and coming from the mining of extensive proteomics data sets 2-5 . These experimental challenges have precluded the direct in vivo probing and full understanding of the bases of fidelity in higher eukaryotes, and their influence in complex processes such as aging. Here we measured proteome-wide misincorporation frequencies in two experimentally tractable eukaryotic systems, yeast and mouse, using mass spectrometry. We find translation fidelity is organism and organ specific. The measured error frequencies correlate with codon:anticodon pairing thermodynamics and tRNA pool composition, which can have synergistic or opposing effects on fidelity depending on organism or tissue type. Most identified protein errors carry a negative fitness burden. Aging experiments in our two systems reveal that, with age, error frequencies increase in post-mitotic cells, but not so in mitotic ones. These changes correlate with remodeling of the tRNA pool, which we identify as a crucial regulator of translation fidelity during lifespan.