Plays a central role in 2-thiolation of mcm(5)S(2)U at tRNA wobble positions of tRNA(Lys), tRNA(Glu) and tRNA(Gln). Directly binds tRNAs and probably acts by catalyzing adenylation of tRNAs, an intermediate required for 2-thiolation. It is unclear whether it acts as a sulfurtransferase that transfers sulfur from thiocarboxylated URM1 onto the uridine of tRNAs at wobble position. tRNA modification; 5-methoxycarbonylmethyl-2-thiouridine-tRNA biosynthesis. Required for normal germline maturation and for viability. Viable at 20 degrees Celsius. At a higher temperature (25 degrees Celsius), the hatched eggs progress through the L1-L4 larval stages with kinetics similar to those of wild type but present an important delay in germline maturation. Whereas gravid wild-type worms are present 53 hours after hatching, germline maturation are still ongoing in the mutant after 66 hours, and the first adults containing eggs are observed 75 hours after hatching, when a large number of new L1 are already present in the wild type. Strikingly, the eggs that finally appeared in the mutant display aberrant morphology and size resulting in both low progeny and high mortality. Belongs to the TtcA family. CTU1/NCS6/ATPBD3 subfamily.