Catalyzes the ATP-dependent 2-thiolation of cytidine in position 32 of tRNA, to form 2-thiocytidine (s(2)C32). The sulfur atoms are provided by the cysteine/cysteine desulfurase (IscS) system. AH2 + ATP + cytidine(32) in tRNA + S-sulfanyl-L-cysteinyl-[cysteine desulfurase] = 2-thiocytidine(32) in tRNA + A + AMP + diphosphate + H(+) + L-cysteinyl-[cysteine desulfurase] Binds 1 [4Fe-4S] cluster per subunit. The cluster is chelated by three Cys residues, the fourth Fe has a free coordination site that may bind a sulfur atom transferred from the persulfide of IscS. tRNA modification. Homodimer. The thiolation reaction likely consists of two steps: a first activation step by ATP to form an adenylated intermediate of the target base of tRNA, and a second nucleophilic substitution step of the sulfur (S) atom supplied by the hydrosulfide attached to the Fe-S cluster. Belongs to the TtcA family.