Figure 3.

Model of eukaryotic elongation. Elongation is depicted as three main stages: (1) During the decoding step, eEF1A•GTP recruits the appropriate aminoacyl-transfer RNA (aa-tRNA) to the A site of the ribosome. Productive recruitment occurs through initial binding and accommodation steps. The accommodation step requires the hydrolysis of eEF1A-bound GTP, followed by release of eEF1A•GDP. The rate of decoding can be reduced by the presence of rare codons. Following its release, eEF1A•GDP is recycled by the guanine nucleotide exchange factor (GEF) activity of eEF1B. (2) Peptide bond formation between the aa-tRNA in the A site and the peptidyl-tRNA in the P site is catalyzed by the ribosomal RNA (rRNA) through different substeps (not shown). The rate of peptide bond formation is affected by recruitment of eIF5A. (3) The translocation step moves the mRNA relative to the ribosome by one codon. This step requires the recruitment of eEF2•GTP, followed by GTP hydrolysis and release of eEF2•GDP. Potential sources of regulation for each step are summarized in boxes and described in more detail in the main text.