PUS3 catalyzes the modification (isomerization) of uridine to pseudouridine at nucleotides 38 and 39 in the anticodon loops of tRNAs (Shaheen et al. 2016). Homologues of PUS3 in mouse (Chen and Patton 2000) and yeast (Lecointe et al. 1998) catalyze the same reaction, and both the PUS3 gene family and the modification are highly conserved. Deletion of DEG1 encoding Pus3p in budding yeast (Saccharomyces cerevisiae) causes slow growth (Lecointe et al. 1998) while a truncating mutation in human PUS3 causes a reduction in pseudouridines 38 and 39 with consequent intellectual disability (Shaheen et al. 2016).