Acts as a positive activator of the GCN2 protein kinase activity in response to amino acid starvation (PubMed:15937339). Forms a complex with EIF2AK4/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 EIF2AK4/GCN2, and hence stimulating EIF2AK4/GCN2 kinase activity (By similarity). Participates in the repression of global protein synthesis and in gene-specific mRNA translation activation, such as the transcriptional activator ATF4, by promoting the EIF2AK4/GCN2-mediated phosphorylation of eukaryotic translation initiation factor 2 (eIF-2-alpha/EIF2S1) on 'Ser-52', and hence allowing ATF4-mediated reprogramming of amino acid biosynthetic gene expression to alleviate nutrient depletion (PubMed:24333428). Interacts with EIF2AK4/GCN2; this interaction stimulates the EIF2AK4/GCN2 kinase activity and is impaired by IMPACT upon a variety of stress conditions, such as amino acid depletion, UV-C irradiation, proteasome inhibitor treatment and glucose deprivation (PubMed:24333428). Interacts with IMPACT; this prevents the interaction of GCN1 with EIF2AK4/GCN2 and inhibits EIF2AK4/GCN2 kinase activity (PubMed:15937339, PubMed:22404850). Associates with ribosomes in undifferentiated neuroblastoma cells and increases after neuronal differentiation (PubMed:23447528). Expressed in the hypothalamus, cortex and hippocampus (PubMed:15937339). Belongs to the GCN1 family.