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In eukaryotes and archaea, the heterotrimeric translation initiation factor 2 (e/aIF2) is pivotal for the delivery of methionylated initiator tRNA (Met-tRNAi) to the ribosome. It acts as a molecular switch that cycles between inactive (GDP-bound) and active (GTP-bound) states. Recent studies show that eIF2 can also exist in a long-lived eIF2γ–GDP–Pi (inorganic phosphate) active state. Here, four high-resolution crystal structures of aIF2γ from Sulfolobus solfataricus are reported: aIF2γ–GDPCP (a nonhydrolyzable GTP analogue), aIF2γ–GDP–formate (in which a formate ion possibly mimics Pi), aIF2γ–GDP and nucleotide-free aIF2γ. The structures describe the different states of aIF2γ and demonstrate the conformational transitions that take place in the aIF2γ `life cycle'.

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Portable Document Format (PDF) file https://doi.org/10.1107/S1399004713032240/mn5043sup1.pdf
Supporting Information.

PDB references: aIF2γ–GDP, 4m0l; nucleotide-free aIF2γ, 4m2l; aIF2γ–GDP–formate, 4m4s; aIF2γ–GDPCP, 4m53


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