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). May act by forming a heterodimer with tut-1/ctu-1 that ligates sulfur from thiocarboxylated urm-1 onto the uridine of tRNAs at wobble position