Fig. 9.

Model of the 48S PIC containing bound eIF1, eIF1A, mRNA, and initiator tRNA. The model is based on directed hydroxyl radical mapping of mammalian eIF1 (127) and eIF1A (228) on 40S subunits and the crystal structure of bacterial 70S elongation complexes containing mRNA and P-site tRNA. The orientation of the tRNA and its location deep in the P site shown here might differ significantly from the eukaryotic scanning 43S or 48S PICs. The image in B is rotated 90° clockwise about the vertical axis from that in A, and the ribosomal protein S13/RpS18e in the head is not shown because it blocks the view of the eIF1A CTT. Ribbon representations of eIF1 are shown in lilac, and the eIF1A domains are shown in blue (OB fold), red (helical domain), green (NTT), and yellow (CTT). mRNA (gold) and tRNA (copper) are shown in the bottom panel only. (Reproduced from reference 228 by permission of Oxford University Press.)