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 ctu1/atpbd3 that ligates sulfur from thiocarboxylated urm1 onto the uridine of tRNAs at wobble position. tRNA modification; 5-methoxycarbonylmethyl-2-thiouridine-tRNA biosynthesis. Belongs to the CTU2/NCS2 family.