This group consists of Eukaryotic TruB proteins similar to Saccharomyces cerevisiae Pus4. S. cerevisiae Pus4, makes psi55 in the T loop of both cytoplasmic and mitochondrial tRNAs. Psi55 is almost universally conserved. Pseudouridine synthases catalyze the isomerization of specific uridines in an RNA molecule to pseudouridines (5-ribosyluracil, psi).