The guanine nucleotide-exchange factor, eIF-2B

摘要: Abstract Eukaryotic initiation factor eIF-2B catalyses the exchange of guanine nucleotides on another translation factor, eIF-2, which itself mediates binding initiator Met-tRNA to 40S ribosomal subunit during initiation. promotes release GDP from inactive [eIF-2·GDP] complexes, thus allowing formation active [eIF-2·GTP] species subsequently binds Met-tRNA. This nucleotide-exchange, step, and activity, are known be an important control point for The activity can modulated in several ways. best characterised these involves phosphorylation α-subunit eIF-2 by specific protein kinases regulated particular ligands. Phosphorylation eIF-2α leads inhibition eIF-2B. mechanism is involved under a variety conditions, including amino acid deprivation yeast (Saccharomyces cereviseae) where it causes translational upregulation transcription GCN4, virus-infected animal cells, kinase activated double-stranded RNA. There now also growing evidence direct regulation appears likely involve its largest subunit. Under certain circumstances may allosteric mechanisms. heteropentamer (subunits termed α, β, γ, δ ϵ) more complex than most other nucleotide-exchange factors. genes encoding all five subunits have been cloned (exploiting GCN4 regulatory system): but α appear essential activity. However, this confer sensitivity phosphorylation. cDNAs ϵ mammalian sources. substantial homology between sequences. Attention directed towards understanding roles individual function