Ancient phylogenetic signal in the sequence of tRNA and their associated aminoacyl-tRNA synthetase (aaRS) enzymes. (a) Unrooted ToL derived from tRNA sequences with their alloacceptor distances traced in thermal scale (from [130]). is average of pairwise distances for 190 pairs of tRNA isoacceptors. These distances measure pairwise sequence mismatches of tRNAs for every genome and their values increase for faster evolving sequences of species of more recent origin. (b) Coevolution of aaRSs and their corresponding tRNA. Genetic distances between the top 10 potentially paralogous aaRS pairs estimated using BLASTP define a measure () of how closely the proteins resemble each other in genomes (from [131]). Larger scores imply more ancestral and slowly evolving protein pairs. The plot of scores against distances reveals a hidden correlation between the evolution of tRNA and aaRSs and the early origin of Archaea (larger and lower distances).
