GCN2 kinase-mediated upregulation of ubiquitin C maintains intracellular glutamine level and tRNA (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 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 in tRNA (CUG) charging levels. Thus, tRNA charging is sensitive to intracellular nutrient status and is an important initiator of intracellular signaling.