Perseverance of protein homeostasis despite mistranslation

Transfer RNAs (tRNAs) are essential for protein synthesis and translation fidelity. Some human tRNA variants may cause amino acid misincorporation: tRNAGly variants (tRNAGlyCCC, tRNAGlyGCC) have mutations that generate an alanine tRNA identity element (G3:U70), likely causing mis-aminoacylation of glycine tRNAs with alanine, while the tRNAAlaAGC G35C (tRNAAlaACC) variant may function similarly to mis-incorporate Ala at Gly codons by generating a Gly anticodon. I propose that these mistranslating tRNAs will disrupt protein homeostasis in mammalian cells. Although the tRNAGly and tRNAAla variants did not affect protein synthesis in normal growth conditions, tRNAGlyGCC A3G depressed protein synthesis following proteasome inhibition. Mass spectrometry confirmed Ala mistranslation at multiple Gly codons caused by the tRNAGlyGCC A3G and tRNAAlaAGC G35C variants. Multiple mistranslation events were also observed within the same peptide. These data reveal mistranslation of Ala at Gly codons that is caused by natural human tRNA variants and tolerated under normal conditions