Pseudokinase domain, repeat 1, of eukaryotic translation Initiation Factor 2-Alpha Kinase 4 or General Control Non-derepressible-2
The pseudokinase domain shows similarity to protein kinases but lacks crucial residues for catalytic activity. EIF2AKs phosphorylate the alpha subunit of eIF-2, resulting in the overall downregulation of protein synthesis. eIF-2 phosphorylation is induced in response to cellular stresses including virus infection, heat shock, nutrient deficiency, and the accummulation of unfolded proteins, among others. There are four distinct kinases that phosphorylate eIF-2 and control protein synthesis under different stress conditions: GCN2, protein kinase regulated by RNA (PKR), heme-regulated inhibitor kinase (HRI), and PKR-like endoplasmic reticulum kinase (PERK). GCN2 is activated by amino acid or serum starvation and UV irradiation. It induces GCN4, a transcriptional activator of amino acid biosynthetic genes, leading to increased production of amino acids under amino acid-deficient conditions. In serum-starved cells, GCN2 activation induces translation of the stress-responsive transcription factor ATF4, while under UV stress, GCN2 triggers transcriptional rescue via NF-kappaB signaling. GCN2 contains an N-terminal RWD, a degenerate kinase-like (repeat 1), the catalytic kinase (repeat 2), a histidyl-tRNA synthetase (HisRS)-like, and a C-terminal ribosome-binding and dimerization (RB/DD) domains. The degenerate pseudokinase domain of GCN2 may function as a regulatory domain. The GCN2 subfamily is part of a larger superfamily that includes the catalytic domains of serine/threonine kinases, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase.
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