GSE112643
Effects of single amino acid deficiency on mRNA translation are markedly different for methionine versus leucine
Amino acid availability regulates translation through the action of the GCN2 and mTORC1 pathways. Low amino acids activate the eIF2a kinase GCN2 through binding of uncharged tRNAs to a histidyl-tRNA synthetase-related regulatory domain. Once activated GCN2 phosphorylates eIF2a, inhibiting ternary complex formation and translation initiation. Recent studies show that mTORC1 is particularly sensitive to arginine and leucine status, with a deprivation of these amino acids leading to a strong inhibition of mTORC1 that prevents the phosphorylation and inactivation of the translational repressor 4EBP1. Though amino acids are known regulators of translation, the effects that deficiencies of specific amino acids have on translation have yet to be determined. We demonstrate that deprivation of leucine or methionine results in large inhibitory effects on translation initiation and on polysome formation that are not replicated by overexpressing non-phosphorylatable 4EBP1 or a phosphomimetic eIF2a. Our results demonstrate that a lack of either leucine or methionine has a major impact on mRNA translation, though they act by quite different mechanisms. Leucine deprivation appears to primarily inhibit ribosome loading, whereas methionine deprivation appears to primarily impair start site recognition. These data point to a unique regulatory effect that methionine status has on translation initiation. Overall design: Ribosome profiling of single Amino acid starvation