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Etude comparative de couples ARNt/aminoacyl-ARNt synthétases chez la levure et la mitochondrie humaine.

Abstract : My work has focused on the specific recognition of transfer RNAs (tRNAs) by aminoacyl-tRNA synthetases (aaRSs), an obligate prerequisite for translation fidelity. I have taken advantage of molecular biology strategies, based on in vitro transcribed tRNAs and cloned enzymes, to explore the structure/function relationships of yeast and human mitochondrial (mt) aminoacylation systems using large mutagenic analyses. Structural and functional aspects were further tackled by crystallization assays and in vivo approaches, respectively.
So far, it was believed that recognition and aminoacylation rules of isoacceptor tRNAs from a given organism are identical. Investigation of the family of arginine isoaccepting tRNAs in yeast and its peculiar relationship with tRNAAsp lead me to the following
discoveries: (i) isoacceptors are aminoacylated with different efficiencies (~20 fold range) and are protected from mischarging by idiosyncratic antideterminants, (ii) isoacceptor tRNA4
Arg is a remnant aspartate acceptor since only two point mutations were sufficient to convert its specificity - this is a direct example of genesis of molecular diversity from a common ancestor. Aminoacylation systems of mammalian mitochondria remain under-explored despite their tRNAs, coded by mt genome, are structurally "bizarre" and involved in severe disorders.
Our efforts lead to the assignment of 10 missing nuclear genes coding for human mt aaRSs, which turned out to be encoded by a different set of genes than the one for cytosolic aaRSs.
Detailed analysis of the aspartylation system, chosen as a model mt system, revealed (i) less stringent identity of a mt tRNA than of classical tRNAs, (ii) a subtle and focused adaptation of the bacterial-type nuclear-encoded mt AspRS. This illustrates co-evolutionary processes of the human mt and nuclear genomes. Further, I have uncovered the signals hindering a mt
tRNAAsp to be a substrate for a non-mt aaRS. Strikingly, it is not the global structural degeneracy of the tRNA which hinders the most cross-aminoacylation, but a single base-pair in the D-stem.
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https://tel.archives-ouvertes.fr/tel-00139137
Contributor : Isabelle Martin <>
Submitted on : Thursday, March 29, 2007 - 2:49:03 PM
Last modification on : Thursday, April 23, 2020 - 2:26:32 PM
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Aurélie Fender. Etude comparative de couples ARNt/aminoacyl-ARNt synthétases chez la levure et la mitochondrie humaine.. Biologie cellulaire. Université Louis Pasteur - Strasbourg I, 2005. Français. ⟨tel-00139137⟩

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