The heterotrimeric archaeal IF2 orthologue of eukaryotic translation initiation factor 2 consists of the α-subunit, β-subunit and γ-subunit. Previous studies showed that the γ-subunit of aIF2, besides its central role in Met-tRNAi binding, has an additional function: it binds to the 5'-triphosphorylated end of mRNA and protects its 5'-part from degradation. Competition studies with nucleotides and mRNA, as well as structural and kinetic analyses of aIF2γ mutants, strongly implicate the canonical GTP/GDP-binding pocket in binding to the 5'-triphosphate end of mRNAs. The biological implication of these findings is being discussed.
Keywords: GTP; a/eIF2γ; archaea; crystal structure; mRNA.
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