Aminoacyl-tRNA synthetases (aaRSs) are ancient and universally essential enzymes that pair tRNAs with the corresponding amino acids. To enhance accuracy, many aaRSs employ an editing activity that hydrolyzes incorrectly activated amino acids. Editing significantly decreases the frequency of mistakes in vitro, although the physiological role of editing in cells remains unknown, as aaRS editing functions are dispensable under certain conditions and absent in some cell types. Through a combination of genetic and physiological tests, we will determine under what conditions aaRS editing is required for viability. Specifically, we will test the hypothesis that editing is required under conditions of extreme slow cell growth.