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. 1997 Sep 15;11(18):2396–2413. doi: 10.1101/gad.11.18.2396

Figure 7.

Figure 7

 Schematic diagram of how GTP hydrolysis controls AUG selection during ribosomal scanning in wild-type cells and SUI suppressor mutants. (A,B) Translation initiation in wild-type cells. When the 43S preinitiation complex (including eIF-2 ⋅ GTP, eIF-3, 40S ribosomal subunit, and the initiator-tRNA) pauses at a non-AUG codon, such as UUG, GTP hydrolysis is inhibited or not induced attributable to the absence of the stringent 3-bp codon/anticodon signal and no translation initiation occurs. Therefore, the ribosome continues to scan the leader and encounters an AUG start codon (B). A 3-bp codon/anticodon interaction occurs, which signals the eIF-5-dependent hydrolysis of GTP bound to eIF-2. Translation initiation factors are released leaving the initiator-tRNA in the P site and the 60S ribosome joins such that elongation can begin. (C,D) Translation initiation at a non-AUG codon in SUI3, SUI4, and SUI5 strains. The 43S preinitiation complex pauses at a UUG codon, a mutation in eIF-5 or eIF-2β allows GTP to be hydrolyzed without a 3-bp codon/anticodon interaction between the UUG and the initiator-tRNA (C). Alternatively, when the 43S preinitiation complex pauses at UUG, the mutation in eIF-2γ results in dissociation of eIF-2 from the initiator-tRNA (D). Either event results in leaving the initiator-tRNA at the P site mismatched base-paired with the UUG codon. The 60S ribosome joins and the ribosome is committed to the elongation phase of translation. (Inline graphic) Initiator tRNA; (➋) eIF-2; (➌) eIF-3; (Inline graphic) eIF-5; (Inline graphic) the 40S ribosomal subunit; (Inline graphic) the 60S ribosomal subunit.