Figure 4.

The eIF3a-NTD functionally interacts with the 5′ sequences of uORF1 to ensure efficient resumption of scanning. (A) Schematic showing predicted position of the 40S ribosome terminating at the stop codon of uORF1 from the GCN4 mRNA leader (data adapted from Wang and Sachs 1997). E, P, and A sites of the 40S ribosomes are aligned with the last two coding triplets and the TAA stop codon. Location of the eIF3a-NTD-responsive site (eIF3a-RS), linker, and buried parts of the sequences upstream of uORF1 are indicated at the top; 3′ boundary of the Δ40 deletion (identical to Δ160), Δ46 deletion, and the (C)₄GG multiple substitution are shown below the line depicting mRNA. (B–F) Same as in Figure 3B, except that YBS47 and YBS53 were transformed with p209, pBS64, pBS62, pVM11, and pBS63, respectively, and analyzed without 3-AT treatment. Activities relative to wild type are given in bold in the table to the left of schematics. (G) a/tif32-Δ8 does not affect GCN4-lacZ expression after translating the REI-nonpermissive uORF4. YBS47 and YBS53 were transformed with pA80z and analyzed as in Figure 3B.