a [protein]-S-sulfanyl-L-cysteine + uridine34 in tRNA + ATP + reduced acceptor = a [protein]-L-cysteine + 2-thiouridine34 in tRNA + AMP + diphosphate + acceptor
a [protein]-S-sulfanyl-L-cysteine + uridine34 in tRNA + ATP + reduced acceptor = a [protein]-L-cysteine + 2-thiouridine34 in tRNA + AMP + diphosphate + acceptor