19 Proofreading by some aminoacyl- tRNA synthetases increases the fidelity of protein synthesis The identity of the amino acid attached to a specific tRNa is not checked by the ribosome(ala-tRNaCyS experiment) The calculated rate of incorrect incorporation of val in place of lle is I in 200, but the observed is only I in 3000. Some synthetases are able to proofread the incorrectly incorporated similar amino acids(e.g, between Val and Ile) at the aminoacyl-AMP stage or the aminoacyl tRNA stage19. Proofreading by some aminoacyl￾tRNA synthetases increases the fidelity of protein synthesis • The identity of the amino acid attached to a specific tRNA is not checked by the ribosome (Ala-tRNACys experiment). • The calculated rate of incorrect incorporation of Val in place of Ile is 1 in 200, but the observed is only 1 in 3000. • Some synthetases are able to proofread the incorrectly incorporated similar amino acids (e.g., between Val and Ile) at the aminoacyl-AMP stage or the aminoacyl￾tRNA stage