Translational regulator that ensures constant high levels of translation upon a variety of stress conditions, such as amino acid starvation, UV-C irradiation, proteasome inhibitor treatment and glucose deprivation. Plays a role as a negative regulator of the EIF2AK4/GCN2 kinase activity; impairs GCN1-mediated EIF2AK4/GCN2 activation, and hence EIF2AK4/GCN2-mediated eIF-2-alpha phosphorylation and subsequent down-regulation of protein synthesis (PubMed:15937339, PubMed:23447528, PubMed:24333428). May be required to regulate translation in specific neuronal cells under amino acid starvation conditions by preventing GCN2 activation and therefore ATF4 synthesis (PubMed:15937339, PubMed:23447528). Through its inhibitory action on EIF2AK4/GCN2, plays a role in differentiation of neuronal cells by stimulating neurite outgrowth (PubMed:23447528). Interacts with GCN1; prevents the interaction of GCN1 with EIF2AK4/GCN2 and inhibits EIF2AK4/GCN2 kinase activity (PubMed:15937339, PubMed:22404850). Interaction with RPL39; this interaction occurs in a GCN1-independent manner (PubMed:22404850). Associates with ribosomes; this interaction occurs in a GCN1-independent manner (PubMed:22404850). Associates with actin; this interaction occurs in a GCN1-independent manner (PubMed:22404850). Present in neurons in most areas of the brain. Present at high level in hypothalamus, particularly in the suprachiasmatic nucleus (at protein level) (PubMed:15937339, PubMed:18260151). Preferentially expressed in brain, with a weaker expression in other tissues (PubMed:9256468). Detected in embryos at 7, 11, 15, and 17 dpc. At 16 dpc, predominantly expressed in the central nervous system (at protein level). Strongly up-regulated during brain development from 17 dpc up to at least postnatal days 14 (at protein level). In N2a neuroblastoma cell line model and in primary cultures of hippocampal neurons, up-regulated during neuronal differentiation induced by serum reduction (at protein level). Up-regulated after serum withdrawal during neuronal differentiation (PubMed:23447528). The Impact locus is imprinted. Paternal inherited gene is expressed, while the maternal inherited gene is silenced. In contrast with most imprinted genes, neighboring genes are apparently not imprinted. Belongs to the IMPACT family.