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For as long as living things have been building proteins based on the code carried by messenger RNA molecules, aminoacyl-tRNA synthetases have been there. These enzymes, AARSs for short, link transfer RNAs (tRNAs) to the corresponding amino acids. That would seem to be a big enough job for one class of enzymes—and when protein-based life began, it was. But as organisms became more complex, AARSs picked up additional domains that allow them to do much more.
“By the time you get to humans, the synthetase has become highly decorated” with those additional domains, says Paul Schimmel, a Scripps Research Institute biochemist who studies these add-on jobs.
Living things possess at least one type of AARS molecule for each of the 20 proteinogenic amino acids. For some amino acids, there are two varieties, with a separate enzyme for use in protein translation that takes ...
