It would seem most efficient for aminoacyl tRNA synthetases (aaRSs) to be attached to ribosomes or anchored at endoplasmic reticulum) so that tRNAs can be immediately charged and reused. However, in cynobacteria, only valyl-tRNA is anchored on the thylakoid membrane, while all other aaRSs are in the soluble portion of the cytoplasm (e.g., Santamaria-Gomez et al. 2016). I should appreciate definite references that characterize cellular localization of aaRSs in all three domains of life (but mammals in particular).