Aminoacyl-tRNA synthetases (aaRSs) are among the most ancient proteins, widespread in all kingdoms of life, and requested for every translation machineries. Their evolutionary histories have been investigated at numerous instances, showing diverses phylogeny and evolutionary schemes at a global level. However, investigation on evolutionnary traces at the residue level remains to be done, in order to address questions about specific adaptive signals within aaRS sequences in response to an ad hoc environment, as for instance the mitochondrial context. Indeed, organellar aaRSs have undergone peculiar and idiosyncratic evolutionary histories due to the endosymbiotic origin(s) of their ancestor, and likely as a result from the massive transfer of genes from the endosymbiont to the host, and/or additional lateral gene transfer events (Brindelfalk et al., 2007). Therefore, the 2 questions we are addressing in the present work are: the deciphering of i) the evolutionary traces (eukaryotic- or bacterial- reminiscences) of aaRSs of mitochondrial location,  and ii) the molecular traces of their adaptation to the mitochondrial environment. 
	To do so, multiple alignments of complete sequences of aaRSs taken from the complete genome of 93 organisms covering the tree of life heve been build and munually adjusted for the 20 aaRSs systems. After sequence clusterisation, an original and innovative approach using a new formalism of “discriminants” has been set up and hosted in a novel software (Ordalie, Ordered alignment information explorer; under-development). 

        “Discriminants” are positions (single residues or blocks of residues) differentially conserved within multiple sequence alignments clusters inside a family. They may contribute to the global evolutionary history (if being consubstantial to the branches of the phylogenic tree), or may enlighten  “cryptic” or “specialized” evolutionary histories (if not resolving the phylogenic tree). “Discriminants” have been exhaustively searched for and combined to invariant residues within the 20 aaRS families, so that to decipher the adaptive messages imposed by the mitochondrial environment. Their display on 3D structures is, as well, a formidable tool to anticipate functional outcomes, and allows for i) identifying/recovering patterns in classical aminoacylation function (substrate-interacting façade), ii) identifying/recovering patterns involved in oligomerization (intra-molecules façade), iii) identifying intra-molecular networks that are contributing to allosteric functional communications (trans-façade residues), and iv) identifying novel patterns related to unraveled partnership/function (non-interaction façade).
        Perspectively, any specific adaptive signals can be searched for by our strategy. Additionally, positions supposedly sensitive to pathology-related mutations (in e.g. vertebrates sequences) are ultimately likely to be predicted.