Aminoacyl-tRNA synthetases are a class of enzymes that charge tRNAs with their cognate amino acids. FARSA is similar to the catalytic subunit of prokaryotic and Saccharomyces cerevisiae phenylalanyl-tRNA synthetases (PheRS). This protein has been shown to be expressed in a tumor-selective and cell cycle stage- and differentiation-dependent manner, the first member of the tRNA synthetase gene family shown to exhibit this type of regulated expression.