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

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Prokaryotic elongation factor EF-Tu delivers aminoacyl-tRNAs to the ribosomal A-site.
• Eukaryotic initiation factor eIF2 binds methionyl-tRNA(i)(Met) to the 40S ribosomal subunit's P-site.

Purpose of the Study:

• To map the binding sites of Saccharomyces cerevisiae eIF2 on the ribosome and Met-tRNA(i)(Met).
• To elucidate the distinct mechanisms of tRNA binding between eIF2 and EF-Tu.

Main Methods:

• Directed hydroxyl radical probing experiments.
• Biochemical analyses.

Main Results:

• eIF2γ primarily contacts the acceptor stem of Met-tRNA(i)(Met).
• A key binding interface was identified between eIF2γ domain III and 18S rRNA helix h44.
• eIF2γ domain III is crucial for ribosome binding, unlike EF-Tu's analogous domain which binds tRNA.

Conclusions:

• Eukaryotic eIF2 and prokaryotic EF-Tu exhibit substantially different tRNA binding mechanisms despite structural similarities.
• The tRNA-binding domain III of EF-Tu appears to have evolved a new ribosome-binding function in eIF2γ.