文档介绍：18. The anticodon and/or the amino acid arms of a tRNA are key for a specific aminoacyl-tRNA synthetase to recognize
This was revealed via: crystal structure determination of the plexed with their cognate tRNAs; parison of tRNAs binding to the same synthetase; and mutagenesis studies.
When the anticodon of tRNAVal is changed from UAC to CAU, the mutated tRNAVal can be recognized by Met-tRNA synthetase and generating a Met-tRNAVal.
When the 3:70 base pair on the amino acid arm of tRNACys is changed from from to , the mutated tRNACys is able to carry Ala, instead of Cys.
A “microhelix” containing only 24 of the 76 nucleotides of tRNAAla is recognized and aminoacylated by Ala-tRNA synthetase.
Positions (green and
orange) of
nucleotides involved
in recognition
between tRNAs and
aminoacyl-tRNA
synthetases.
A single G=U base pair is the only
element needed for specific binding
of tRNAAla and aminoacylation by
Ala-tRNA synthetase
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 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 (., between Val and Ile) at the aminoacyl-AMP stage or the aminoacyl-tRNA stage.
There seems to be separate proofreading active site (s) on such synthetases.
In a few synthetases that activate amino acids having no close structural relatives, no such proofreading activities have yet identified (selected at the substrate binding level).
The codon on mRNA is recognized by the anticodon
of tRNA rather than by the activated amino acid
1. Cys-tRNACys is chemically converted to Ala-tRNACys ;
2. Studies with in vitro protein synthesis systems proved
that Ala-tRNACys will incorporate Ala at places of Cys:
using poly(