Acts as a positive activator of the EIF2AK4/GCN2 protein kinase activity in response to amino acid starvation. 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. 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. 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. Interacts with IMPACT; this prevents the interaction of GCN1 with EIF2AK4/GCN2 and inhibits EIF2AK4/GCN2 kinase activity. Associates with ribosomes in undifferentiated neuroblastoma cells and increases after neuronal differentiation. Ubiquitously expressed (PubMed:9039502). Expressed in skeletal muscules, ovary and testis (PubMed:9234705). Belongs to the GCN1 family. Extended N-terminus.