Responsible for synthesis of pseudouridine from uracil-54 and uracil-55 in the psi GC loop of transfer RNAs. uridine(54) in tRNA = pseudouridine(54) in tRNA uridine(55) in tRNA = pseudouridine(55) in tRNA Optimum temperature is 70 degrees Celsius. Belongs to the pseudouridine synthase Pus10 family.