Fig. (8).

Hypothetical model for the mechanism of unwinding of mRNA and scanning by the 48S PIC. The small ribosomal subunit is viewed from the solvent face in a gray semi-transparent surface with the rRNA backbone shown as ribbon; the mRNA is illustrated as red solid ribbon. Schematic shows the PIC-associated factors and/or their particular domains including eIF4E and the 4E-BR, the HEAT1, HEAT2 and HEAT3 domains of eIF4G, the CTD and RRM domains of eIF4H, and the NTD and CTD of eIF4A. The direction of scanning of the initiation complex along the mRNA (5' to 3') is indicated by an arrow; eIF4A is shown on the leading (3') side of the scanning complex.