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Nat Struct Mol Biol. 2011 Oct 16;18(11):1227-34. doi: 10.1038/nsmb.2133.

Initiation factor eIF2γ promotes eIF2-GTP-Met-tRNAi(Met) ternary complex binding to the 40S ribosome.

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Laboratory of Gene Regulation and Development, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, USA.


In contrast to prokaryotic elongation factor EF-Tu, which delivers aminoacyl-tRNAs to the ribosomal A-site, eukaryotic initiation factor eIF2 binds methionyl initiator transfer RNA (Met-tRNA(i)(Met)) to the P-site of the 40S ribosomal subunit. The results of directed hydroxyl radical probing experiments to map binding of Saccharomyces cerevisiae eIF2 on the ribosome and on Met-tRNA(i)(Met) revealed that eIF2γ primarily contacts the acceptor stem of Met-tRNA(i)(Met) and identified a key binding interface between domain III of eIF2γ and 18S rRNA helix h44 on the 40S subunit. Whereas the analogous domain III of EF-Tu contacts the T stem of tRNAs, biochemical analyses demonstrated that eIF2γ domain III is important for ribosome, not Met-tRNA(i)(Met). Thus, despite their structural similarity, eIF2 and EF-Tu bind tRNAs in substantially different manners, and we propose that the tRNA-binding domain III of EF-Tu has acquired a new ribosome-binding function in eIF2γ.

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