43S pre-initiation complex contains
Eukaryotic 43S pre-initiation complex represents key intermediate before mRNA recruitment, comprising 40S small subunit bound to eIF1, eIF1A, eIF3 multi-subunit complex, eIF5, and ternary complex eIF2 GTP Met-tRNAiMet positioned in P site. Assembly occurs independently of mRNA and ensures initiator tRNA ready to base-pair with start codon. This complex interacts with eIF4F capped mRNA to form 48S scanning complex. Formation of ternary complex is rate-limiting regulated by eIF2 alpha phosphorylation during integrated stress response reducing global initiation while permitting selective ATF4 translation.
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 7, 43S pre-initiation complex containing 40S, eIFs, Met-tRNAi