GCN2 kinase-mediated upregulation of ubiquitin C maintains intracellular glutamine level and tRNA Gln (CUG) charging under amino acid starvation.

Each tRNA is aminoacylated (charged) with a genetic codon-specific amino acid. It remains unclear what factors are associated with tRNA charging and how tRNA charging is maintained. By using the individual tRNA acylation PCR (i-tRAP) method, we found that the charging ratio of tRNA (CUG) reflects cellular glutamine level. When uncharged tRNA (CUG) increased under amino acid starvation, the kinase GCN2, which is a key stimulator of the integrated stress response, was activated. Activation of GCN2 led to the upregulation of ubiquitin C (UBC) expression. Upregulated UBC, in turn, suppressed the further reduction of tRNA (CUG) charging levels. Thus, tRNA charging is sensitive to intracellular nutrient status and is an important initiator of intracellular signaling.