Translational control of gene expres- sion is generally exerted in the initia- tion phase of protein synthesis. The reac- tions of the initiation pathway bring the ribosome to the mRNA and place the initiation codon in the peptidyl (P) site of the ribosome, base-paired with the anti- codon of methionyl initiator tRNA (Met- tRNA). The aminoacyl (A) site in the ribosome is left open to accept the elon- gator tRNA that decodes the second codon in the ORF. Formation of this 80S initiation complex in eukaryotic cells de- pends on 11 or more soluble initiation factors (eIFs), identified primarily through biochemical studies of translation in rabbit reticulocyte extracts.
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