Intron positions delineate the evolutionary path of a pervasively appended peptide in five human aminoacyl-tRNA synthetases.

Recent progress in genome sequencing has revealed a correspondence between the evolution of multicellularity and the appending of new peptides onto age-old enzyme bodies. Indicative of the pervasive nature of these appended peptides, in some cases the same sequences have been appended to a number of different enzymes. By analyzing the positions of introns within one such roaming peptide, an approximately 50-amino acid motif appended to five human aminoacyl-tRNA synthetases, I have delineated its path in eukaryote evolution. The motif was first acquired as an N-terminal extension by histidyl- and glycyl-tRNA synthetases at a very early stage of eukaryote evolution. Later, but not less than 1200 million years ago, the motif spread from histidyl-tRNA synthetase to the C and N terminals of glutamyl- and prolyl-tRNA synthetase, respectively, and then spread further during the evolution of the Chordate lineage to the N terminal of tryptophanyl-tRNA synthetase. In similar fashion, the motif in glycyl-tRNA synthetase spread to the C terminal of methionyl-tRNA synthetase not later than 1000 million years ago.