Catalyzes the 2-thiolation of uridine at the wobble position (U34) of mitochondrial tRNA(Lys), tRNA(Glu) and tRNA(Gln). Required for the formation of 5-taurinomethyl-2-thiouridine (tm5s2U) of mitochondrial tRNA(Lys), tRNA(Glu), and tRNA(Gln) at the wobble position. ATP is required to activate the C2 atom of the wobble base. 5-taurinomethyluridine(34) in tRNA + AH2 + ATP + S-sulfanyl-L-cysteinyl-[protein] = 5-taurinomethyl-2-thiouridine(34) in tRNA + A + AMP + diphosphate + H(+) + L-cysteinyl-[protein] Present with 1510 molecules/cell in log phase SD medium. During the reaction, ATP is used to activate the C2 atom of U34 by adenylation. After this, the persulfide sulfur on the catalytic cysteine is transferred to the C2 atom of the wobble base (U34) of mitochondrial tRNA(Lys), tRNA(Glu) and tRNA(Gln). The reaction probably involves hydrogen sulfide that is generated from the persulfide intermediate and that acts as nucleophile towards the activated C2 atom on U34. Subsequently, a transient disulfide bond is formed between the two active site cysteine residues (By similarity). Belongs to the MnmA/TRMU family. Was originally thought to be a 5-methylaminomethyl-2-methyltransferase involved in tRNA modification.