Acts as a positive activator of the GCN2 protein kinase activity in response to low amino acid, carbon, or purine availability (PubMed:8497269, PubMed:24333428. PubMed:10733573). Component of the GCN1-GCN20 complex that forms a complex with GCN2 on translating ribosomes; during this process, GCN1 seems to act as a chaperone to facilitate delivery of uncharged tRNAs that enter the A site of ribosomes to the tRNA-binding domain of GCN2, and hence stimulating GCN2 kinase activity (PubMed:7621831, PubMed:9234705, PubMed:15722345). Participates in the repression of global protein synthesis and in gene-specific mRNA translation activation, such as the transcriptional activator GCN4, by promoting the GCN2-mediated phosphorylation of eukaryotic translation initiation factor 2 (eIF-2-alpha/SUI2) on 'Ser-52', and hence allowing GCN4-mediated reprogramming of amino acid biosynthetic gene expression to alleviate nutrient depletion (PubMed:8497269, PubMed:10801780, PubMed:11350982, PubMed:15722345). Interacts (via N- and C-terminus) with GCN2 (via N-terminal RWD domain); this interaction stimulates GCN2 kinase activity in a GCN20-dependent manner in response to amino acid starvation (PubMed:10775272, PubMed:11101534, PubMed:10801780, PubMed:11350982, PubMed:15126500, PubMed:15722345, PubMed:21849502). Interacts (via C-terminus) with GCN20 (via N-terminus); this interaction stimulates GCN2 kinase activity in response to amino acid starvation (PubMed:7621831, PubMed:9234705, PubMed:11101534). The GCN1-GCN20 complex interacts with GCN2 on translating ribosomes in amino acid-starved cells; GCN1 may bind near the ribosomal A-site and promotes the transfer of uncharged tRNAs from the A-site to the tRNA-binding domain in GCN2 for its subsequent kinase activation, and hence allowing GCN4 translational activation and derepression of amino acid biosynthetic genes (PubMed:7621831, PubMed:9234705, PubMed:10775272, PubMed:11101534). Interacts (via C-terminus) with YIH1 (via N-terminus); this interaction reduces the GCN1-GCN20 complex formation and prevents the interaction of GCN1 with GCN2 and GCN2 kinase activation in amino acid-starved cells (PubMed:15126500, PubMed:21239490, PubMed:22404850). Interacts with GIR2; this interaction prevents the interaction of GCN1 with GCN2 and GCN2 kinase activation in amino acid-starved cells (PubMed:19448108). Interacts (via middle region) with RPS10A and RPS10B; these interactions are direct and promote GCN2 kinase activation (PubMed:25437641). Associates (via N-terminus) with ribosomes; this association is stimulated in a ATP- and GCN20-dependent manner and is necessary to activate GCN2 kinase activity (PubMed:7621831, PubMed:9234705, PubMed:11101534, PubMed:15722345, PubMed:19448108, PubMed:21849502, PubMed:22888004, PubMed:25437641). The EF3-like region is necessary and sufficient for interaction with GCN20 (PubMed:9234705). Inhibits GCN4 derepression in glucose, amino acid, or purine-starved cells. Present with 7330 molecules/cell in log phase SD medium. Belongs to the GCN1 family.