The E-site story: the importance of maintaining two tRNAs on the ribosome during protein synthesis.
In the sixties James Watson suggested a twosite model for the ribosome comprising the P site for the peptidyl transfer RNA (tRNA) before peptide-bond formation and the A site, where decoding takes place according to the codon exposed there. In the eighties a third tRNA binding site was detected, the E site, which was specific for deacylated tRNA and turned out to be a universal feature of ribosomes. However, despite having three tRNA binding sites, only two tRNAs occupy the ribosome at a time during protein synthesis: at the A and P sites before translocation (PRE state) and at the P and E sites after translocation (POST state). The importance of having two tRNAs in the POST state has been revealed during the last 25 years, showing that the E site contributes two fundamental features: (i) the fact that incorporation of a wrong amino acid is not harmful for the cell (only 1 in about 400 misincorporations destroys the function of a protein) stems from the presence of an E-tRNA; (ii) maintenance of the reading frame is one of the most remarkable achievements of the ribosome, essential for faithful translation of the genetic information. The presence of the POST state E-tRNA prevents loss of the reading frame.
Wilson
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AG Ribosomen, Max-Planck-Institut für Molekulare Genetik, Ihnestr 73, 14195, Berlin, Germany.
Nierhaus
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D019943:Amino Acid Substitution; D000596:Amino Acids / Q000378:metabolism; D001665:Binding Sites; D005057:Eukaryotic Cells / Q000378:metabolism; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D010441:Peptide Chain Elongation, Translational; D011387:Prokaryotic Cells / Q000378:metabolism; D014176:Protein Biosynthesis; D012343:RNA, Transfer / Q000737:chemistry / Q000378:metabolism*; D012346:RNA, Transfer, Amino Acyl / Q000378:metabolism; D016364:Reading Frames; D012270:Ribosomes / Q000737:chemistry* / Q000378:metabolism*
D000596:Amino Acids; D012346:RNA, Transfer, Amino Acyl; D012343:RNA, Transfer