2.8.1.4	ATP + [ThiI sulfur-carrier protein]-S-sulfanyl-L-cysteine + uracil in tRNA + 2 reduced ferredoxin [iron-sulfur] cluster = AMP + diphosphate + 4-thiouracil in tRNA + [ThiI sulfur-carrier protein]-L-cysteine + 2 oxidized ferredoxin [iron-sulfur] cluster	a group of enzymes transferring sulfur to various nucleotides in a tRNA chain, producing residues such as 4-thiouridylate. With some enzymes mercaptopyruvate can act as sulfur donor	-	
2.8.1.4	ATP + [ThiI sulfur-carrier protein]-S-sulfanyl-L-cysteine + uracil in tRNA + 2 reduced ferredoxin [iron-sulfur] cluster = AMP + diphosphate + 4-thiouracil in tRNA + [ThiI sulfur-carrier protein]-L-cysteine + 2 oxidized ferredoxin [iron-sulfur] cluster	on enzyme activation, an alpha-helix overhanging the active site is restructured into an idiosyncratic beta-hairpin-containing loop, which packs the flipped-out U34 deeply into the catalytic pocket and triggers the activation of the catalytic cysteine residues. The adenylated RNA intermediate is trapped. The active closed-conformation of the complex ensures accurate sulfur incorporation into the activated uridine carbon by forming a catalytic chamber to prevent solvent from accessing the catalytic site	676149