CTU2 is a family of proteins necessary for the formation of the wobble nucleoside 5-methoxycarbonylmethyl-2-thiouridine in Saccharomyces cerevisiae. The family is conserved from plants to humans ]1]. It plays a central role in the 2-thiolation of 5-methoxycarbonylmethyl-2-thiouridine, or the wobble nucleoside. This wobble modification in tRNAs, 5-methoxycarbonylmethyl-2-thiouridine (mcm(5)s(2)U), is required for the proper decoding of NNR codons in eukaryotes. The 2-thio group gives rigidity by largely fixing the C3'-endo ribose puckering, ensuring stable and accurate codon-anticodon pairing.