 43S PIC assembly is believed to be stimulated by the initiation factors eIF1, eIF1A, and the eIF3 complex according to "in vitro" experiments.The 43S PIC then binds mRNA that has previously been unwound by the eIF4F complex.The 43S PIC and the eIF4F proteins form a new 48S complex on the mRNA, which starts searching along the mRNA for the start codon (AUG).