Initiation of protein synthesis in eukaryotes

Unlike prokaryotes, the Met-tRNAi is pre-bound to the 40S subunit, i.e. it’s binding is not codon-directed. The mRNA is SCANNED to find the first AUG. The ATP requirement is for the helicase activity of eIF-4A to remove hairpin structures in the mRNA. Polysomes in electron micrographs are often observed to be circular. Poly (A) tail greatly stimulates rate of protein synthesis. Poly (A) tail binds poly (A) binding protein (PAB1). PAB1 interacts with eIF4G and eIF4E bound to “cap”. Ribosomes that have completed translation dissociate into subunits. These can readily find the nearby m7G cap and initiate another round of protein synthesis. Rapid recycling of subunits increases the efficiency of translation.