Evidence for Late Resolution of the AUX Codon Box in Evolution |
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Authors: | Thomas E Jones Lluís Ribas de Pouplana Rebecca W Alexander |
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Institution: | From the ‡Department of Chemistry, Wake Forest University, Winston-Salem, North Carolina 27109-7486.;the §Institute for Research in Biomedicine, C/Baldiri reixac 10, Barcelona 08208, Catalonia, Spain, and ;the ¶Institució Catalana de Reserca I Estudis Avançats, Passeig Lluís Companys 1, Barcelona 08010, Catalonia, Spain |
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Abstract: | Recognition strategies for tRNA aminoacylation are ancient and highly conserved, having been selected very early in the evolution of the genetic code. In most cases, the trinucleotide anticodons of tRNA are important identity determinants for aminoacylation by cognate aminoacyl-tRNA synthetases. However, a degree of ambiguity exists in the recognition of certain tRNAIle isoacceptors that are initially transcribed with the methionine-specifying CAU anticodon. In most organisms, the C34 wobble position in these tRNAIle precursors is rapidly modified to lysidine to prevent recognition by methionyl-tRNA synthetase (MRS) and production of a chimeric Met-tRNAIle that would compromise translational fidelity. In certain bacteria, however, lysidine modification is not required for MRS rejection, indicating that this recognition strategy is not universally conserved and may be relatively recent. To explore the actual distribution of lysidine-dependent tRNAIle rejection by MRS, we have investigated the ability of bacterial MRSs from different clades to differentiate cognate tRNACAUMet from near-cognate tRNACAUIle. Discrimination abilities vary greatly and appear unrelated to phylogenetic or structural features of the enzymes or sequence determinants of the tRNA. Our data indicate that tRNAIle identity elements were established late and independently in different bacterial groups. We propose that the observed variation in MRS discrimination ability reflects differences in the evolution of genetic code machineries of emerging bacterial clades. |
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Keywords: | Aminoacyl tRNA Synthesis Aminoacyl tRNA Synthetase Enzymes Phylogenetics Protein Synthesis Transfer RNA (tRNA) Anticodon Genetic Code Evolution Translational Accuracy |
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